THE FAUNA OF THE ST. .JOHN (illOUP. 



41 



seen to consist of line wavy stria?, which often present an obliquely reticulated appearance, 

 or when viewed in the line of the concentric striœ appear to consist of granulations ; in 

 some examples, the granulated appearance is obscure and the valves are more regularly 

 striate. 



The substance of the shell in this species is phosphatic as iu Lingulella and Linnars- 

 sonia, and the inner layers are smooth and separate easily, so that the outer and inner sur- 

 faces of the valves are less frequently exposed in breaking the matrix in which the shells 

 are embedded than are these smooth intermediate layers. The outer layer of the shell, 

 which is granulated and striated, appears to be prismatic. 



Varieties. 



Acrothele MaUhewi is one of those variable species which, without the intermediate 

 forms, might be divided into several ; the above description applies to the type, but th(n-e 

 are two distinct varieties having the following characters : — 



Viir. a. Piii.MA. (Plate V. Figs. 16 and 16«). 



Valves flat, one fifth wider than long ; test thin, ventral valve concave iu the middle, 

 umbo at the posterior margin, granulations nearly uniform over the whole surface. 



Var. fi. LATA. (Plate V. Figs. 1*7 and Via) 



Apex directed upward, one third wider than long, umbo of the ventral one fifth from 

 the posterior margin, which is nearly straight in the middle half; flattened marginal part 

 of the dorsal is crescentiform and narrower than iu the type ; outer surface of the valves 

 not known. 



MEASUREMENTS OF THE TYPE OF ACROTHELE MATTHEWI AND THE VARIETIES (IN 



MILLIMETRES.) 



Sec. IV., 1885. 0. 



