CYTHERE. 167 



from above, ovate, widest in the middle ; extremities obtusely mucronate, margins 

 irregular. The carapace of the male is longer, narrower, and distinctly quadrangular, 

 its greatest height situated in front and equal to less than half the length ; superior 

 margin distinctly angular over the anterior hinge, behind which it is slightly 

 excavated, and then slopes backwards almost in a straight line ; posterior margin 

 obliquely truncate. Shell-surface deeply marked with irregular angular excavations, and 

 with three or more prominent obliquely transverse ribs. Hinge-teeth strongly 

 developed. 



Length, -^th of an inch. 



C. costata has been found living amongst the Shetland Islands and in Baffin's 

 Bay, at a depth of 60 — 70 fathoms. It is very nearly allied to C. emarginata, 

 being distinguished from that species chiefly by its greater size and narrower proportions, 

 as well as by its prominent obHque ridges, and the dentation of its infero-posterior angle. 



Distribution. Becent. — Arctic Seas, Shetland, Gulf of St. Lawrence. 



Fossil. — England : Bridlington, Hopton Cliff. Scotland : Paisley. 



35. Cythere mirabilis, Brad^. Plate VII, figs. 22—26 ; Plate XV, figs. 13— 16. 



1868. Cythere mirabilis, Brady. Monog. Rec. Brit. Ostrac, p. 415, pi. xxix, 



figs. 7, 8. 



Carapace of Vi\q female, as seen from the side, subtrapezoidal, highest at the anterior 

 third, greatest height equal to two thirds of the length. Anterior extremity broad, 

 boldly rounded, and bordered below with a series of ten to twenty short, blunt spines ; 

 posterior narrow, truncate, bearing about four blunt spines at its inferior angle. 

 Superior margin prominently angular over the anterior hinge, behind which it is two 

 or three times deeply and abruptly excavated, thence sloping with a steep, irregularly 

 jagged curve to the posterior extremity, where it ends in an obtuse angle; inferior 

 margin gently and evenly convex. Outline, as seen from above, ovate, with flattened 

 sides, width equal to more than half the length : posterior extremity rounded, 

 prominent in the middle, and bearing numerous sharp, irregularly placed spines ; anterior 

 margin obtuse, irregularly denticulate or spinous. Surface of the shell sculptured on the 

 central and centro-dorsal portions with large, deep, and sharply cut polygonal excavations, 

 and round the margins with wide, concentric furrows, which are separated from each 

 other by sharp ribs, sparingly anastomosing, and especially strong and prominent 

 on the ventral surface. Hinge-joint formed on the left valve by a very strong central bar, 

 terminating anteriorly in a prominent tooth, and posteriorly in a sharply defined sulcus ; 

 on the right valve by two very large terminal teeth, the anterior of which is triangular 



