354 CARBONIFEROUS LAMELLIBRANCHIATA. 



in front, but almost straight for its posterior two thirds. The posterior border is 

 truncated obliquely from above downwards and forwards, and is straight, so that 

 the postero-superior angle projects further backwards than any other part of the 

 shell. The postero-inferior aDgle is blunt and obtuse, the postero-superior angle 

 almost a right angle, and is well marked. The superior border is much arched in 

 front, and is almost straight posterior to the umbones. The umbones are small, 

 pointed, twisted forwards, contiguous, and are placed very far forwards, being 

 encroached upon in front by a large lunule. Passing obliquely backwards and 

 downwards from the umbo to the postero-inferior angle is a blunt, obtuse, but 

 well-defined ridge separating the shell into two unequal portions : the anterior or 

 larger is very gently convex ; the posterior is compressed, expanded and hollowed, 

 forming the dorsal slope. The escutcheon is large, and becomes wider and deeper 

 as it passes backwards. 



Interior. — The anterior adductor muscle-scar is small and deep, situated 

 immediately within the anterior superior angle, and separated from the rest of 

 the shell by a ridge, which leaves a groove in casts. The posterior adductor scar 

 is small and shallow, and is placed a little within the margin of the posterior 

 superior angle. Pallial line entire. The hinge of the right valve consists of a 

 thin anterior lamellar tooth, with a hollow groove above it for the corresponding 

 tooth of the opposite valve, a cardinal tooth with a socket in front and behind it, 

 and a long lamellar posterior lateral tooth. 



Exterior. — The surface is ornamented with fine concentric lines of growth, and 

 an occasional one so much accentuated that it forms a well-marked sulcus. 



Localities. — Scotland : the Upper Limestone series of Gare, Robroyston. 

 The Lower Limestone series of Craigen Glen ; Law, Dairy. Roscobie and Daloch 

 Quarry, Fife. 



Dimensions. — Fig. 30, PI. XXXIX, measures — 



Antero-posteriorly . . . .13 mm. 



Dorso-ventrally . . . .10 mm. 



Elevation of valve .... 2*5 mm. 



Observations. — This species was established for a specimen from the Limestone 

 of Vise in 1842 by de Koninck, and re-described in 1885, a single figure only being 

 given. In the meanwhile de Ryckholt {op. supra cit.) had described under the 

 genus Trapezium two shells, also from the limestone of Vise, which I have no doubt 

 are synonymous with C. Selysiana. De Koninck retained the three species, 

 referring them to the genus Sanguinolites, and says in his observations on the 

 latter species it is closer to 8. prsesectus and S. Lyellianus than any other, and 

 is distinguished from the former by its rectangular shape, and from the latter by 

 having the umbones placed not so far forward and by the prolongation of its 

 anterior end below them. A large series of examples shows that these characters 



