280 DR. A. E. TEUE3IAN OX THE [vol. lxxiv. 



a diameter of 7 mm. a body -chamber already equal in length to 

 more than three -quarters of a whorl. The inner whorls are smooth, 

 and costse are not acquired until the diameter of 3 mm. is reached. 

 From this stage onwards the whorl becomes more elevated. Sutural 

 development similar to that in Amblycoceras crescens, which will 

 be next described : thus denticulations appear in each species at 

 the same diameter and in the same order, and the sutures are 

 remarkably similar (text-fig. 10 b & c, p. 283). 



)iarueter. 



Whorl height. 





Whorl thickness. 



Umbilicus. 



mm. 



per cent. 





per cent. 



per cent. 



0-7 



50 





75 



— 



1'4 



43 





55 



35 



3-0 



42 





60 



33 



4-7 



40 





51 



32 



7-5 



37 





40 



33 



currence. 



— Latcecosta 



sub 



-zone, Brick-Pit, 



Pilley, Leek 



hampton. 



Distinction : Suture and lib-curve distinguish A. brevilobatum 

 from all species except A. crescens, which differs in having a stouter 

 form. 



With A. brevilobatum occur somewhat more advanced specimens 

 having the outer whorl expanded, bituberculation commencing 

 (S. S. JBuckman Coll. No. 2817). This may be Microceras sinu- 

 osum Hyatt (2, p. 82), which is described as a bituberculate form 

 with peripheral rib-curve ; Mr. Buckman placed this species with 

 Oistoceras, 1 but Hyatt refers to the shallow first lateral lobe of 

 its suture, a character which suggests Amblycoceras. 



Amblycocebas ceescexs Hvatt. (PI. XXIY, figs, la-lb & 

 2a-2b; text-figs. 9 & 10 b, pp. 281, 283.) 



Compare Mgoceras capricomum Geyer. 2 

 Dimensions of specimen figured here : — 



Diameter. Whorl height. Whorl thickness. Umbilicus. 



32 mm. 31 per cent. 34 per cent. 40 per cent. 



A small Capricorn, with stout thick whorls ; ribs very prominent 

 on the sides and periphery, where they have a forward bend. Bibs 

 of the last whorl widely spaced (18 to the whorl). 



Suture fairly simple ; first lateral lobe very shallow ; external 

 lobe with broad and short median saddle (fig. 10 b, p. 283). 



Hyatt named this species, but gave no figure ; and the name has 

 not been generally used. The specimen here figured agrees with 

 Hyatt's description in having a shallow ' superior ' lateral lobe and 

 stout whorl. 



1 ' The Geology of the Country between Whitby & Scarborough ' Mem. 

 Geol. Surv. 2nd ed. (1915) p. 96. 



2 G. Geyer, ' Die Mittelliasische Cephalopoden-Fauna des Hinter-Schaf- 

 berges in Ober-(Esterreich ' Abhandl. K.-K. Geol. Eeichsanst. vol. xv (1893) 

 pt. 4, pi. iii, fig. 9. 



