OF THE ANTWEEP CEAG. 391 



greatest width in the middle and fully equal to half the length. End view subtri- 

 angular with convex sides, nearly equilateral. Surface of the shell slightly undulated, 

 devoid of sculpture, except that a thin curved alBeform ridge is developed towards the 

 ventral margin of each valve ; the anterior margin bears below the middle a variable 

 number of short, blunt, irregular spines : and there are usually two or three of similar 

 character at the posterior extremity of the shell ; the lateral ala often has a single spine 

 a little behind the middle ; and the ventral surface of the shell is more or less marked 

 with flexuous longitudinal grooves. Length -^ inch (1-3 millim.). 



Cythere tarentina has not preAdously been observed in the fossil condition ; but it still 

 lives in many parts of the Mediterranean. It is a very distinct and fine species. Several 

 specimens have been found in the sand from the Panopcea- and Pectunculus-heAB. 



Cytheee acuticosta, Egger. (Plate LXVI. figs. 5 a-5 d.) 

 Cythere acuticosta, Egger, op. cit. p. 40, pi. vi. fig. 7. 



Carapace, as seen from the side, rhomboidal, equal in height throughout ; height 

 equal to nearly two thirds of the length ; anterior margin obliquely rounded off ; posterior 

 obliquely truncate below the middle, rounded off above ; dorsal margin straight ; ventral 

 also straight, except the anterior half, which is a little upturned. Seen from above, the 

 outline is elongated, subhexagonal or subovate, sides nearly parallel but irregularly 

 flexuous, width equal to half the length, tapering rather abruptly towards the extre- 

 mities, which are pointed. End view quadrangular with irregularly waved sides, width 

 equal to three fourths of the height. The surface of the shell is strongly sculptured 

 with sharply cut ridges, running for the most part in a longitudinal direction, but 

 irregularly flexed and anastomotic; one of them, more developed than the rest, is in 

 the median line ; the furrows between these ridges are excavated into pits of very 

 irregular size and shape ; the dorsal surface is marked by a very distinct longitudinal 

 median groove with raised ridges ; and the ventral surface has on each valve a flattened 

 alaeform plate which is sculptured with transverse and marginal excavations. Length 

 -^ inch (0'54 millim.). 



Our specimens of this species occurred in the Pectuncidus- and Panojycea-heds. 

 Though the figures given by Dr. Egger differ rather considerably (especially in the end 

 view) from my own, I am disposed to think that they are meant to refer to the same 

 species, and on that supposition have adopted the specific name acuticosta. 



Cytheee trapezia, nov. sp. (Plate LXVI. figs. 4 a-4 d.) 

 ? Cythere corrugata, Egger, op. cit. p. 35, pi. v. fig. 3. 



Carapace, as seen laterally, trapezoidal, rather higher in front than behind, height 

 equal to more than half the length ; anterior extremity obliquely rounded ; posterior 

 subtruncate, rounded a little below, the lower angle not produced ; dorsal and ventral 

 margins nearly straight, the latter very gently situated in the middle. The outline from 



