SUPPLEMENT.— DISSOROCERAS. cxv 



the outer part is so much more bowed in Deltoidoceras, (2) by the cross section — in 

 Deltoidoceras, subtriangulate, in Dissoroceras, subquadrate ; (3) by earlier decline of 

 costate stage in Dissoroceras. 



The character of the periphery enables these genera to be separated from Lucya 

 and Depaoceras ; but this character is not inconsistent with close relationship 

 thereto. It is almost certain that the carinati-tabulate periphery is polyphyletic. 



Subfalciradiate. 

 XL VII. Genus — Dissoroceras, 1 8. Buckman. 



(Type : Dissoroceras tabulation, S. Buckman.) 

 1902. Dissoroceras, Emend. Amm. Norn., p. 3. 



Definition. — Platysubleptogyral, subaugustumbilicate (subdensiseptate, sublongi- 

 angustilobate) 3 ; laterally anguli- to flexi-radiate ; peripherally sublatanguliradiate, 

 tabulate, subalticarinate. (Radial line, Fig. 76, p. clxv.) 



1. Dissoroceras tabulatum, 8. Buckman. Plate XXI, figs. 5, G; Suppl., Fig. 76,. 



p. clxv. 



1889. Ludwigia Lucti, This Monogr., PI. xxi, figs. 5, 6 only. 

 1902. Dissoroceras tabulatum, Emend. Amm. Nom., p. 5. 



Description. — Subcrassi-subobscuricostate to levigate with age; subgradum- 

 bilicate. 



Bernards.— Smoothness appears with some rapidity, so that in a specimen 

 111 mm. in diameter the costate umbilicus is the only indication of the costate 

 youth. 



Locality and Stratum. — Dorset: Bradford Abbas, Fossil Bed, presumably upper 

 part. 



Date of Existence — Discitae hemera, presumably. 



2. Dissoroceras subornatum, 8. Buckman. Suppl., Fig. 77 in text. 



Description. — Gradumbilicate, connaticostate, declining early to levigate. 



Remarks. — Inner whorls show costae connate near to the inner margin. The 

 costse decline to become obscure and subdistant. Smoothness of test commences at 

 about 38 mm. diameter. 



Distinction. — From D. tabulatum, more compressed whorls, a smaller, Less 

 costate, umbilicus, earlier commencement of smoothness. 



1 Itrjni.Q, double ; opoQ, border. 



2 Seen imperfectly on a specimen of D. tabulatum. 



