CYTHERURA. 195 



which are sometimes angularly areolated. Shell of the male more compressed and more 

 angular in outline. 



Length, -^vA of an inch. 



There is much diversity in the development of the surface-ornament in this species, 

 some specimens show^ing scarcely more than a mere undulation of the surface (fig. 12), 

 while others (fig. 9) are very distinctly ridged and occasionally even areolated in the 

 interspaces. It is, perhaps, next to C. niyrescens, the commonest fossil species of 

 the genus. 



Distribution. Recent. — Baffin's Bay, Gulf of St. Lawrence, Spitzbergen, Norway, 

 Great Britain, Ireland. 



Fossil. — Scotland : nearly all the Post- tertiary beds. Ireland : New Docks at 

 Belfast, Portrush. Norway. Canada. 



S. Cytherura compressa, nov. sp. Plate XI, figs. 21 — 23. 



Carapace subrhomboidal, higher in front than behind, greatest height more than 

 equal to half the length, situated in front of the middle; anterior extremity obliquely 

 rounded ; posterior angularly produced in the middle ; superior margin arched ; inferior 

 almost straight. Seen from above, subpentagonal, acuminate in front, mucronate 

 behind, width less than the height. End-view pentagonal, widest in the middle, 

 the base concave, with a central keel. Surface of the shell obsoletely striated. 

 Length, -^i\\ of an inch. 



Distribution. Fossil. — Scotland : Gamrie. 



9. Cytherura striata, G. 0. Sars. Plate XI, figs. 38 — 41. 



1865. Cytherura striata, G. 0. Sars. Overs. Norg. mar. Ostrac, p. 74. 

 1868. — — Brady. Monog. Rec. Brit. Ostrac, p. 441, pi, xxxii, 



figs. 26—29, 62, 64, 65. 



Carapace, as seen from the side, compressed, oblong, of nearly equal height throughout, 

 height equal to less than half the length ; anterior extremity rounded, posterior produced 

 in the middle into along beak ; superior margin forming a flattened arch, inferior sinuated 

 in the middle. Seen from above, the outline is subpentagonal, with parallel sides, pointed 

 in front and strongly mucronate behind, width about equal to the height. End-view 

 subtriangular, widest at the base, which is centrally keeled. Surface marked with 



