8 



obtusely pointed umbo, whose lateral margins are obliquely convex : 

 its beak is small and very slightly incurved, and its hinge area is broad, 

 as measured from its anterior to its posterior margin, and shallowly 

 crescentic. 



The dorsal or brachial valve is about as convex as the ventral, but 

 its cardinal area is compai-atively narrow from back to front : the 

 crown of the crescent is regularly arched and parallel with the front 

 margin of the cardinal area, and on each side the crescent terminates 

 in a small subpyriform scar. The platform is scarcely raised above the 

 lowest level of the valve posteriorly, and is bounded at the sides and in 

 front by a V-shaped raised ridge, whose pointed base is dii-ected for- 

 wards. The middle muscular scars of the platform are broadly rounded 

 on their inner margins, which latter nearly touch each other in the 

 centre. On their outer margins the middle scars are bounded by the 

 posterior half of the V-shaped ridge which has already been described 

 as forming the lateral and anterior boundary of the platform itself. 

 The anterior muscular scars occupy or are placed upon a small sub- 

 rhomboidal or somewhat lozenge-shaped area on the platform in front 

 of the middle. 



As compared with Messi-s. Davidson's & King's figure of the pedicle 

 valve of the " Trimerella (?) Galtensis" of their paper,* the umbones 

 and beaks of the ventral valves described above are not so much pointed 

 nor so flatly conical in their lateral outline, and theii- cardinal areas are 

 crescentic rather than triangular. 



The markings on the interior of the dorsal valve from Dui-ham 

 described above are essentially the same as those on the mould of the 

 brachial valve of the Trimerella Galtensis of Messrs. Davidson's & King's 

 paper, though in the Durham specimen the crown of the crescent seems 

 to be regularly rounded in the middle and not pointed. 



The generic name Bhynoholus (Hall, 1871,) as applied to the present 

 species, is adopted here in accordance with a suggestion to that effect 

 recently made to the writer by ilr. Davidson. In a letter received in 

 November, 1883, IMi-. Davidson says :—" Although with much uncer- 

 tainty this shell was placed by Prof King and myself in the o-enus 

 Trimerella, it is not a true Trimerella and should be removed from that 

 genus. It is more closely allied to Mmovierella, and perhaps it would 

 be better to retain Prof Halls generic name oi Bhynoholus for its recep- 

 tion.' 



* On the Trimerellidse. Quart. Journ. Geol. Soc. Lond. Vol. XXX, pi. 18, 

 fig. 13. 



