1872.] HICKS XREMADOC ROCKS. 47 



Homfrayi has no spines at the angles, nor has it a strong margin to the 

 head. The positions of the anterior and posterior ocular furrows are 

 different in the two species ; and the tail in the Niobe Homfrayi also 

 has a less number of furrows, both on the axis and the lobes. The 

 labrum, too, is wider, and has a better-defined margin. 

 Loc. Kamsey Island, and Tremanhire, St. David's. 



Niobe solvensis, spec. nov. PI. IV. figs. 10-16. 



This is a small species, from an inch to an inch and a half in length. 

 General shape a broad oval. Head semicircular, with posterior 

 spines reaching backwards to about one half of the length of the 

 thorax. Margin throughout strong, and wide at the sides, but nar- 

 rowing anteriorly opposite the glabella. Glabella occupying a third 

 of the width of the head, widest anteriorly ; grooved by four or five 

 short and faint lateral furrows, and a neck furrow. Eyes situated 

 halfway up the head, semilunar in shape, prominent, and tolerably 

 large. Anterior facial sutures running obliquely forwards, in front of 

 the eyes, and the posterior backwards to cut across the hinder margin 

 about half the distance across from the glabella to the outer edge. 

 Body-axis broad, equally wide throughout, and moderately arched. 

 Pleurae as long as the width of the axis, deeply grooved, and with 

 the fulcrum situated about a third of the distance across from the 

 axis in the anterior ones, but further out in the hinder ones : all 

 bluntly pointed at the ends. 



Tail semicircular, with a strong margin equally wide throughout ; 

 axis well raised, tapering quickly towards the extremity, which is 

 bluntly pointed and prominent over the inner edge of the margin, and 

 marked by ten distinct rings. Lateral lobes wide, and marked by from 

 six to eight ribs, the anterior ones being deep, and the hinder ones faint. 

 This is a much smaller and wider form than the Niobe menapiensis, 

 and is easily distinguished from it by its wide thoracic axis, which 

 is equally broad throughout, and by the wide lateral lobes of the 

 tail. The eyes are also nearer the middle of the length of the head, 

 and larger in proportion to the size of the species. 

 Log. Ramsey Island, and Tremanhire, St. David's. 



Ctexodonta menaptensis, Hicks. PI. V. figs. 6 & 7. 



C. rotunda, Hicks, Cambridge Catalogue. 



Ovate in form, ^ of an inch long by about -^ wide. Valves well 

 raised, beak prominent and pointed, and placed nearer to the anterior 

 margin. Surface marked by fine concentric lines, and ventral margin 

 fimbriated. Both ends of the shell rounded, posterior most ; mus- 

 cular scars strong ; teeth prominent. 



Loc. Ramsey Island and Tremanhire. 



Ctenodonta cambrienbis, Hicks. PI. V. figs. 8 & 9. 



G. elongata, Hicks, Cambridge Catalogue. 



Ovate in form, but nearly equilateral, with the umbo situated 

 almost midway between the extremities ; § of an inch long and 

 rather more than ^ in width. Shell regularly convex, and marked 



