48 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 4, 



by strong lines of growth near the pallial margin. Muscular scars 

 moderately strong, the anterior being most distinct. Teeth not so pro- 

 minent as in C. menapiensis, from which species it is at once distin- 

 guished by its subcentral umbo and nearly equilateral sides. 

 Loc. Ramsey Island and Tremanhire. 



Pal-eakca Hopkinsoni, spec. nov. PL Y. fig. 11. 



Oval in form, half an inch in length, and width rather more than 

 half the length. Hinge-line less than a third of the length. Shell con- 

 vex near the beak, but flattened and spread out anteriorly. The beak 

 does not reach quite to the cardinal margin, and is placed nearer the 

 anterior end. Muscular scars well shown, and lines of growth 

 tolerably distinct. 



Loc. Found by Mr. J. Hopkinson, F.G.S. (after whom I have the 

 pleasure of naming it), at Ramsey Island and St. David's. 



Pal^aeca oboloidea, spec. nov.. PL Y. fig. 10. 



Rather over a third of an inch long and nearly as broad at the 

 widest part. Strongly convex, except near the posterior extre- 

 mity, where it suddenly becomes flattened. Beak subcentral, nearer 

 anterior extremity, and overhanging cardinal margin. Surface 

 marked with strong lines of growth. In its subcentral beak and 

 oboloid outline it differs materially from P. Hoplcinsoni. 



Loc. Eamsey Island and St. David's. 



Gltptaeca, gen. nov. 



Inequilateral and strongly ventricose. Beak near anterior end, 

 prominent, overhanging more or less the hinge-line, and pointed at 

 the extremity. Two diverging ridges extend from the umbo to 

 the margin, and enclose a triangular sulcus having its base at the 

 margin, which it thereby indents. Anterior muscular impression 

 strong, posterior less distinct. Hinge-area narrow, plate thick, with 

 three teeth in front of the umbo. Surface strongly marked (especially 

 near pallial margin) with concentric lines of growth. The strong 

 diverging ridges and deep sulcus indenting the pallial margin, along 

 with the very narrow hinge and raised and strongly produced beak, 

 form the chief characters of this genus, and distinguish it at once 

 from all known Silurian genera. 



Gltptaeca peem^va, spec. nov. PL Y. figs. 1-4. 



Pear-shaped, | of an inch long and about ^ wide. Anterior extre- 

 mity short, posterior long and tapering, beak prominent. Surface 

 deeply grooved from beak to pallial margin, which is strongly indented. 

 Lines of growth strong. Muscular scars well marked. 



Loc. Ramsey Island and Tremanbire, being very plentiful at both 

 places. 



Gltptaeca Lobleti, spec. nov. PL Y. fig. 5. 



Much larger than O. primceva, and it is also wider at the posterior 

 extremity. Half an inch long and about § wide. Hinge-margin 



