184 SILURIAN MOLLUSCA. 



V 



broad backward wave in the middle (about three in the space 

 of 1 Hne) ; sutures deep, simple, sutural angle 100°. Length 



1 inch 11 hnes, length of last whorl 9 lines, width 7| lines. 



The greater length and slenderness of the whorls and the 

 broader and more shallow wave in the strise separate it from the 

 so-called Terebra sinuosa (Sow.). 



In the gray flags of Pont y Meibion ; slates of Llansantfraid, 

 Glyn Ceiriog. 



{Col. University of Cambridge.) 



Turbo crebristria (M'Coy). 



8p. Char. Ovate, of three to four very rapidly enlarging volu- 

 tions ; spire small, apical angle about 90°, whorls convex, with 

 an obtusely bounded narrow concave space at the sutures above, 

 back broad, gently convex ; umbilicus narrow, deep, effuse at 

 the edge, mouth very large, obscurely angulated retrally ; shell 

 thick, surface girt with sharp spiral thread-like ridges, nearly 

 twice their thickness apart, about four in the space of 1 line 

 on the penultimate whorl, with an occasional finer one between 

 a regular pair, all crossed obliquely by very fine, regular, sharp 

 lines of growth. Length (of small perfect specimen) 1 inch, 

 width 1 inch, length of body-whorl 8 lines (grows to nearly 



2 inches in diameter). 



The large casts of this species are smooth, and resemble Sow- 

 erby's figure and description of T. Pricea, except that the back 

 is broad and rather flattened, or shghtly convex instead of being 

 angular in the middle as that species is defined to be. The sub- 

 stance of the shell is thick, and its mode of striation resembles 

 that of the so-called Pleurotomaria bilioc of Conrad as figured by 

 Hall (Palaeontology of New York), which is however distin- 

 guished by its smaller size, longer spire and want of an umbi- 

 licus. 



Common, of large size, in the schists of Gelli Grin, Bala, Me- 

 rionethshire ; in the fine sandy schists of Mandinam, Llan- 

 dovery ; in the fine sandstone of Alt yr Anker, Meifod, Mont- 

 gomeryshire ; and in the limestone of Mynydd Fron Prys, five 

 miles west of Chirk, Glyn Ceiriog. 



{Col. University of Cambridge.) 



Trochus ccelatus (M^Coy). 



Sp, Char. Conical, apical angle 80^ ; spire of three and a half 

 flattened volutions, having a thick rounded keel forming the 

 circumference of the basal whorl^ and close to the suture on 

 the spiral whorls ; base flattened ; surface marked mth oblique 



