The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany) Author Korn, Dieter 286CA4F3-7EBC-4AEF-A66A-B2508D001367 Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, 10115 Berlin, Germany. dieter.korn@mfn.berlin Author Weyer, Dieter A09A1738-C70E-4F22-A069-8B7DB4A1753D Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, 10115 Berlin, Germany. dieter.weyer@t-online.de text European Journal of Taxonomy 2023 2023-07-19 882 1 230 http://dx.doi.org/10.5852/ejt.2023.882.2177 journal article 58033 10.5852/ejt.2023.882.2177 57d1d191-2bf5-4229-a0f5-9ab472a114a6 2118-9773 8177581 67C909E4-C700-4F8D-B8CE-5FD9B2C5D549 Stockumites procedens ( Korn, 1984 ) comb. nov. Fig. 36 ; Tables 30–31 Acutimitoceras procedens Korn, 1984: 80 , pl. 4 figs 24–25, text-fig. 5b. Acutimitoceras procedens – Korn 1994: 47 , text-figs 36b–c, 71f. Acutimitoceras prorsum prorsum – Korn 1981: 519 , text-figs 3a, 4a–d. Diagnosis Species of Stockumites with a conch reaching 40 mm diameter. Conch at 5 mm dm thinly pachyconic, subevolute (ww/dm ~0.65; uw/dm ~0.35); at 15 mm dm thinly pachyconic, involute (ww/dm ~0.65; uw/dm ~0.12); at 30 mm dm thickly discoidal, involute (ww/dm ~0.55; uw/dm ~0.00). Whorl profile at 30 mm dm weakly depressed (ww/wh ~1.05); coiling rate very high (WER ~2.35). Venter very broadly rounded, umbilical margin broadly rounded. Growth lines fine, with convex course in the middle growth stage and slightly biconvex course in the adult stage. Ornament with shallow constrictions on the shell surface; with coarse internal shell thickenings. Material examined Holotype GERMANY • Müssenberg , trench 1; Hangenberg Limestone , bed 3c; Korn 1980 Coll.; illustrated by Korn (1984 : pl. 4 fig. 24) and Korn (1994: text-fig. 36b); GZG .INV.131. Paratypes GERMANY • 1 specimen ; Müssenberg, trench 1; Hangenberg Limestone, bed 3c; Korn 1980 Coll.; GZG .INV.132 • 3 specimens ; same collection data as for preceding; SMF 43141 – SMF 43143 . Fig. 36. Stockumites procedens ( Korn, 1984 ) . A . Specimen MB.C.31088 (Weyer 1993–1994 Coll.) from the Oberrödinghausen railway cutting, bed 6b. B . Cross section of paratype GZG.INV.132 (Korn 1980 Coll.) from the Hangenberg Limestone at Müssenberg(from Korn 1984 ). C–E . Ontogenetic development of the conch width index (ww/dm), umbilical width index (uw/dm), whorl width index (ww/wh) and whorl expansion rate (WER) of specimens from the type locality Stockum and from Oberrödinghausen. Scale bar units = 1 mm. Table 30. Conch measurements, ratios and rates of Stockumites procedens ( Korn, 1984 ) from Müssenberg and Oberrödinghausen.

specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZR
GZG.INV.131	29.6	17.4	17.0	0.0	10.2	0.59	1.02	0.00	2.33	0.40
MB.C.31088	17.6	11.5	8.7	2.1	5.2	0.66	1.33	0.12	2.02	0.40
GZG.INV.132	15.9	9.6	8.5	1.9	4.2	0.61	1.14	0.12	1.84	0.51

Table 31. Conch ontogeny of Stockumites procedens ( Korn, 1984 ) .

dm	conch shape	whorl cross section shape	whorl expansion
2 mm	thinly pachyconic; subevolute (ww/dm ~0.65; uw/dm ~0.40)	moderately depressed; weakly embracing (ww/wh ~1.85; IZR ~0.15)	moderate (WER ~1.95)
5 mm	thinly pachyconic; subevolute (ww/dm ~0.65; uw/dm ~0.35)	moderately depressed; moderately embracing (ww/wh ~1.60; IZR ~0.30)	moderate (WER ~1.95)
15 mm	thinly pachyconic; involute (ww/dm ~0.65; uw/dm ~0.12)	weakly depressed; very strongly embracing (ww/wh ~1.15; IZR ~0.50)	moderate (WER ~1.85)
30 mm	thickly discoidal; involute (ww/dm ~0.58; uw/dm ~0.04)	weakly depressed; moderately embracing (ww/wh ~1.05; IZR ~0.40)	very high (WER ~2.35)

Additional material GERMANY • 1 specimen ; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 6b; Weyer 1993–1994 Coll.; MB.C.31088 . Description Holotype GZG.INV.131 is a very well preserved, complete specimen with 30 mm conch diameter. The conch is thickly discoidal (ww/dm = 0.58); it has a funnel-shaped umbilicus that is completely closed. The aperture is very high and leads to a coiling rate of WER = 2.34. The shell bears very fine, biconvex growth lines with only weakly developed lateral sinus. Four shell constrictions are developed at 90 degrees to each other, restricted to the venter and ventrolateral flank area. The cross-section of the smaller paratype GZG.INV.132 has slightly wider whorls (ww/dm = 0.60) at 16 mm conch diameter. The umbilicus is still open at this stage (uw/dm = 0.12). Specimen MB.C.31088 has a conch diameter of 17.5 mm ( Fig. 36A ) and shows the transition from the middle growth stage to the adult stage, which is characterised by a considerable increase in aperture height. The conch is thinly pachyconic with a slightly opened umbilicus (ww/dm = 0.66; uw/dm = 0.12) and a high coiling rate (WER = 2.02). The shell surface has initially rather coarse and lamellar but later fine growth lines, which extend with a convex arc across the flank and form a shallow subangular sinus on the venter. Weak shell constrictions extend parallel to the growth lines. Remarks Stockumites procedens can easily be distinguished from the other species of the genus by the very high coiling rate in the adult stage. With a value of about 2.35, it exceeds by far the rate (usually under 2.00) known from the other species. Another character to distinguish S. procedens from the other species of the genus is the development of shell constrictions, which extend across the venter with a subangular sinus.