SYNOPSIS OF GENERA. U 



Sanguinolites, McCoy (Carboniferous Fossils of Ireland, p. 47. 1844). 



The following is Prof. McCoy's original description : 



"Transversely oblong, convex, equivalve, very inequilateral. Basal and 

 ventral margins parallel or nearly so. Anterior end short, rounded. Posterior 

 side lengthened, obliquely truncate, gaping. An oblique ridge usually extends 

 from the beak to the anal angle, but no flexure ; ligament external." 



" This genus has been formed to .include a number of fossil shells of the 

 older rocks, hitherto classed with Sanguinolaria. The latter shells have the 

 ventral and dorsal margins curving toward each other posteriorly, forming a 

 sub-mucronate beak-like termination to the posterior end, while on the con- 

 trary, the dorsal and ventral margins of the present shells are nearly parallel, 

 so that the posterior end is as wide or wider than the other parts of the shell ; 

 they are also much more gibbous and have no posterior fold." 



By reference to the figures cited, or given in illustration of the forms of this genus, 

 it will be seen that they are not congeneric, and later authors in adopting the 

 name, and endeavoring to reconcile the difficulties, have not made the 

 matter more clear. On carefully reviewing the subject, and giving due 

 weight to the later expressions of Prof McCoy,* and to the illustrations which 

 he claims to be characteristic species of the genus, I find the reasoning which I 

 adopted fifteen years agof to be untenable, and therefore the group of species 

 then referred to Sanguinolites have received another generic designation. 



One of the characteristic forms of the genus referred to by Prof. McCoy, 

 S. sulcatus, has been made the type of the genus Allorisma by Prof. King ; but 

 there still remains a group of shells with strong concentric ridges or undulations 

 of the surface, which are without posterior fold, or defined umbonal ridge, and 

 cannot be properly referred to Grammysia or Allorisma, but which correspond 

 with some of the forms referred to this genus by its author. 



* British Palffiozaic Fossils, page 276. 1854. 



t Preliminary Notice of the Laraellibrauchiata, 2, page 34. 



