MYTILOMORPHA RHOMBEA. 343 



by the authorities to refigure it, PI. XXXVIII, fig. 8. I have, however, a strong 

 suspicion that the two shells really belong to one species, and that G. glabrata 

 was only the young state of Mytilomorpha rhombea. I have therefore considered 

 it as a synonym, but it would be impossible to retain the species in the absence 

 of the type and any definite description ; for, meagre as were the descriptions 

 generally given by Phillips, he described his G. rhombea as " rhomboidal valves 

 diagonally carinated," and G. glabrata " ovato-rhomboidal valves diagonally 

 tumid." 



In company with Morris, de Verneuil, Etheridge, and others, I regard the 

 C. bvpartita of de Koninck (op. supra cit.) as a synonym of Phillips's shell, 

 although in his later work de Koninck protests against such a view, and says, p. 69, 

 " le 8. rhombeus est relativement plus large, surtout vers son extremite posterieure, 

 que le 8. bipartitus ; parce que le carene diagonale de celui-ci est beaucoup plus 

 arquee, et que son bord anterieur est forme d'une courbe d'un rayon beaucoup plus 

 court." He gives the following comparative dimensions : — 8. rhombeus, \. 30 mm., 

 h. 15 mm., ep. 12 mm. ; 8. bipartitus, 1. 25 mm., h. 12 mm., ep. 14 mm. I do not 

 believe that any useful purpose can be served by tlie erection of species on small 

 differences in comparative measurements, and I would remark that in Belgium 

 both species occur at the same horizon, Etage III, Visean. Judging from the 

 drawing alone there would be some doubt whether de Verneuil's shell is identical 

 with Phillips's, but that author expresses himself in the text as thoroughly 

 convinced upon this point. 



I have placed Solenopsis scapha of de Ryckholt as a possible synonym. This 

 species occurred in the beds at Vise, and the species was adopted by de Koninck, 

 who figures a very young specimen. 



I am also disposed to regard de Koninck's Sanguinolites cuneatus as synonymous 

 with M. rhombea. 



I am of opinion that an error has been made in referring shells, from various 

 localities in the Carboniferous series of the west of Scotland, to the "species by 

 Messrs. Young and Armstrong. I have as yet seen nothing like the shell from 

 these localities, but in Scotch cabinets I find that the name Gypricardia rhombea, 

 Phillips, is applied to those shells which I describe, p. 356, as Gypricardella 

 rectangular is. 



The full-grown example, fig. 11, PL XXXVIII, from the cabinet of Mr. R. 

 Law of Hipperholm, Yorkshire, far exceeds in size any other specimens with 

 which I am acquainted, and serves to emphasise the essential differences between 

 this species and M. angulata. This specimen is a cast of the interior, only in- 

 complete at the postero-superior angle. The details of the anterior part of the 

 hinge are still unknown, and only enough of the posterior hinge-line is left to 

 show a rolled edge and the absence of a lateral tooth. There is no evidence that 



