SILURIAN MOLLUSCA. 185 



scaly ridges. Length 2^ lines, width 4 lines, length of last 

 whorl 1 line. 



Owing to the scaly nature of the ornament on the rather wide 

 oblique ridges of the surface, they usually adhere to the matrix, 

 and breaking off from the shell leave it nearly smooth. 



Very rare in the limestone of Old Radnor, Presteign, Radnor- 

 shire. 



{Col. University of Cambridge.) 



Trochus constrictus (M'Coy). 



Sp. Char. Conical, apical angle about 70°, of four or five gra- 

 dually increasing whorls, each with a shallow concavity or con- 

 striction below the suture, the lower portion strongly rounded, 

 base flattened, circumference obtusely rounded ; surface ob- 

 liquely crossed by fine, unequal, often obscurely fasciculate 

 lines of growth ; mouth transverse, obliquely ovate. Length 

 8 lines, width 7~ lines, length of mouth 3J lines, width of 

 mouth 4 lines. 



This seems allied to the Holopea symmetrica (Hall) of the 

 Trenton limestone, but the spire is not so elevated, the base is 

 more flattened, and the mouth is stated to be almost circular in 

 that species, which besides has the whorls regularly convex from 

 the simple suture. 



In the schists on the Bala limestone, Bryn Melyn quarry near 

 Bala; Cymmerig, Bala, Merionethshire. 



(Col. University of Cambridge.) 



Trochus Moorei (M'Coy). 



Sp. Char. Acutely conical, apical angle 50°, of about five (four 

 preserved) flattened, gradually increasing whorls ; mouth trans- 

 versely subquadrate ; base flattened_, moderately convex ; um- 

 bilicus deep, narrow ; surface unknown. Length about 8 lines, 

 width 6 lines, length of mouth 3 lines, width of mouth 2>~ lines. 



I dedicate this very distinct species to J. Carrick Moore, Esq. 

 (Secretary of the Geological Society), who has devoted much 

 labour to the elucidation of the old fossiliferous rocks of Scot- 

 land. 



In the fine sandstone of Dalquorhan near Girvan, Ayrshire. 



{Col. University of Cambridge.) 



Cucullella (M'Coy), n. g. 



Gen. Char. Subrhornboidal, inequilateral, subequivalve, margins 

 even ; hinge-line entirely crenulated ; muscular impressions 



