LOWER LIAS OF ROBIN HOOD'S BAY 



139 



are large enough to have divided first lateral lobes appear to have the 

 bifid lobes of Leptonotoceras. However, many of the specimens are 

 very small and the largest (in bed 501 .2) is only 19 mm diameter. In the 

 top part of the Taylori Subzone at Robin Hood's Bay the much larger 

 species Gemmellawceras rutilans has the trifid first lateral lobes of 

 Gemmellaroceras s.s. Whether this division into subgenera is real, oris 

 a function of the size to which species grow and therefore the complex- 

 ity attained by their suture-lines, has still to be resolved. 



Gemmellaroceras tubellum (Simpson, 1855) 



1855 Ammonites tubellus Simpson: 42. 

 1876 Aegoceras tubellum (Simpson); Blake: 279. pi. 5, fig. 7. 

 1924 Tubellites tubellus (Simpson); Buckman: pi. 491 (holotype, 

 WM 98 1 ; ?probably from bed 497 or 498). 



RANGE. Beds 495.7-505.1, Macdonnelli to Taylori Subzones; 104 

 specimens. 



Range. After its first appearance in the top bed of the Macdonnelli 

 Subzone, G. tubellum becomes much more common in the Aplanatum 

 and bottom of the Taylori Subzones. 



Gemmellaroceras rutilans (Simpson, 1843) PI. 7, fig. 4 



1843 Ammonites rutilans Simpson: 45. 



1962 Polymorphites rutilans (Simpson); Howarth: 110.pl. 15, 

 figs 7 (neotype (designated Howarth, 1962: 1 10), WM 95), 

 8 ( WM 94); both probably from bed 526. 1 or 530. 1 . 



RANGE. Beds 526. 1 and 530. 1 . Taylori Subzone; 4 specimens. 



Remarks. G. peregrinum (Haug, 1887: 1 14, pi. 4, fig. 5) is a very 

 similar (?or identical) species that occurs in the upper part of the Taylori 

 Subzone in Dorset (bed 108), where specimens attain large sizes of up 

 to 90 mm diameter. 



Genus POLYMORPHITES Haug, 1887 



Polymorphites caprarius (Quenstedt, 1856) 

 1856 



PI. 7, fig. 9 



Ammonites caprarius Quenstedt: 131, pi. 16, fig. 1 (holotype, 



from Balingen, Wurttemberg, Germany; BM C. 55358 is a 



cast of this specimen). 

 1885 Ammonites caprarius Quenstedt: Quenstedt: 244, pi. 30, 



figs 40, 41 (holotype refigured). 

 1976 Platypleuroceras caprarium (Quenstedt); Schlegelmilch: 



63, pi. 29, fig. 5 (holotype refigured). 

 1980 Polymorphites caprarius (Quenstedt); Schlatter: 92. 



Range. Beds 538-542.5, Polymorphus Subzone; 87 specimens. 



Remarks. There seems to be no doubt that Quenstedt's figure of 

 1885 (pi. 30. fig. 41) is a drawing ofthe same specimen that he figured 

 in 1856 (pi. 16, fig. 1). This specimen (Geological Institute, Tubingen 

 University. Ce 5/30/41 ) was figured again by Schlegelmilch (1976); it 

 is the holotype. Schlegelmilch's (1976: 63) designation of this speci- 

 men as neotype was not necessary. One of Bairstow's better preserved 

 specimens from bed 539 is figured in PI. 7, fig. 9. 



Polymorphites trivialis (Simpson, 1843) 



1843 

 1876 



1912 



PI. 7, fig. 7 



Ammonites trivialis Simpson: 10. 



Amaltheus trivialis (Simpson); Blake: 292, pi. 5, figs 6a 



(BM C. 17891), 6b-d. 



Polymorphites trivialis (Simpson); Buckman: pi. 53, figs 1, 



la, lb (the lectotype, WM 105, now lost), figs 2, 3 



(paralectotypes). 



Range. Beds 542.4—546.3, Polymorphus and Brevispina Subzones; 

 84 specimens. 



REMARKS. Many examples of P. trivialis are found in beds 544.35- 

 544.9 at the top of the Polymorphus and bottom of the Brevispina 

 Subzones, and it is highly probable that the type specimens came from 

 544.35, 544.4, 544.5 or 544.9. 



Polymorphites bronni (Roemer, 1836) 



PI. 7, fig. 5 



1836 Ammonites bronni Roemer: 181, pi. 12, fig. 8 (holotype, 



from north Germany). 

 1884 Ammonites bronni Roemer; Quenstedt: 245, pi. 30, figs 44, 



46, 48 (from Wurttemberg, Germany). 

 1976 Polymorphites bronni (Quenstedt); Schlegelmilch: 62, pi. 



28, fig. 8 (original of Quenstedt, 1885: pi. 30, fig. 48). 

 1980 Polymorphites bronni (Quenstedt); Schlatter: 82, pi. 7, fig. 



1, pi. 11, fig. 5 (from Wurttemberg, Germany). 



RANGE. Beds 554—560.3, Jamesoni Subzone; 36 specimens. 



REMARKS. Occurs in the upper half of the Jamesoni Subzone, and it 

 differs from P. trivialis and P. polymorphus in having consistently 

 stronger ribbing, small ventro-lateral tubercles and a mid- ventral keel. 

 The Robin Hood's Bay specimens have been identified from Schlatter's 

 (1980: 82) interpretation ofthe species. 



Polymorphites polymorphus (Quenstedt, 1845) PI. 7, fig. 3 



1845 Ammonites polymorphus quadratus Quenstedt: 87, pi. 4, 

 fig. 9 (lectotype. from Germany, designated by Donovan & 

 Forsey, 1973: 12). 



1961 Polymorphites polymorphus (Quenstedt); Dean el al.\ pi. 

 68, fig. 4 (from Gloucestershire). 



!10 mm diameter. 



PLATE 7 



Fig. 1 Apoderoceras aculeatum (Simpson). Bed 524.3, CA4022. x 0.5; wholly septate up to the aperture at ca. 



Fig. 2 Phricodoceras comutum (Simpson). Bed 525. CA 4070. 



Fig. 3 Polymorphites polymorphus (Quenstedt). Bed 555, CA 43 1 7. 



Fig. 4 Gemmellaroceras rutilans (Simpson). Bed 526.1, CA 4178; approximated adult septa occur at the position marked three-quarters of a whorl before 



the aperture. 

 Fig. 5 Polymorphites bronni (Roemer). Bed 560.3 (below the top 0.08 m). CA 4226: wholly septate. 



Platypleuroceras aureitm (Simpson). Bed 546.2, CA 4480; the body chamber appears to be exactly one whorl long. 

 Polymorphites trivialis (Simpson). Bed 544.35, CA 4326; wholly septate. 

 Aegoceras (A.) maculatum (Young & Bird) var. atavum Spath. Bed 583.2, C. 38874. 



Polymorphites caprarius (Quenstedt). Bed 539, CA 4237; a complete microconch, with a body chamber about two-thirds of a whorl long. 

 Tropidocerasfuttereri Spath. 10, bed 560.3 (in the top 0.08 m), CA 4544. 11, bed 568, CA 4545. 

 Aegoceras (A.) maculatum (Young & Bird). 12, bed 581. C.41307. 13, bed 590.61, C. 38883. 



Fig. 6 



Fig. 7 



Fig. 8 



Fig. 9 



Figs 10, 11 



Figs 12, 13 



Fig. 14 Aegoceras (Oistoceras) sinuosiforme Spath. Bed 598. 1 , C. 38930. 



All figures natural size, except Fig. 1. 



