CYTHERURA. 199 



Carapace of the female, as seen from the side, elongated, subquadrangular, of nearly 

 equal height throughout, height equal to about half the length, rounded in front; 

 posterior margin produced above the middle into an obtuse obliquely truncate beak ; 

 superior margin almost straight ; inferior gently sinuated. Outline, as seen from above, 

 constricted in the middle, the posterior half forming on each side a rounded protuberance, 

 greatest width situated near the posterior extremity and equal to at least half the length ; 

 anterior extremity suddenly tapering, acuminate ; posterior broadly rounded, with a 

 prominent central mucro. End-view pentagonal, width greater than the height. The 

 male more elongated, with the upper margin slightly, the lower deeply, sinuated. The 

 shell is marked, more or less distinctly, with large polygonal reticulations ; ventral 

 surface longitudinally striated. 



Length, -^^\k\ of an inch. 



Distribution. Recent. — Britain, Baltic Sea, North Sea. 



Fossil. — Scotland : West Tarbert, Raised beach at Oban. Ireland : Belfast New 

 Docks, Portrush. 



16. Cytherura cornuta, Brady. Plate XIII, figs. 23 — 25. 



1868. Cytherura cornuta, Brady. Monog. Rec. Brit. Ostrac, p. 445, pi. xxxii, 



figs. 12—15. 



This species differs from the foregoing {C. gihba) chiefly in having an arcuate dorsal 

 margin, a sharper posterior beak, and when viewed from above in being less tumid 

 posteriorly and without any central constriction. The end-view is triangular instead of 

 pentagonal. The shell-sculpture is much the same in both species. It must be 

 admitted, however, that it is not always easy to determine to which of the two forms a 

 given specimen should be referred. 



Distribution. Recent. — Britain, Dardanelles, Levant. 



Fossil. — Scotland : West Tarbert Silt. Norway. 



17. Cytherura acuticostata, G. 0. Sars. Plate XVI, figs. 1 — 3. 



1865. Cytherura acuticostata, G. O. Sars. Overs. Norg. mar. Ostrac, p. 76. 

 1868. — — Brady. Mon. Eec. Brit. Ostr., p. 445, pi. xxxii, 



figs. 1—11. 



Carapace, as seen from the side, quadrate, subrectangular, height equal to half the 



