366 MR. G. S. BRADY ON NEW OR IMPERFECTLY 



myself off the Isle of Man, have the posterior extremity remarkably spinous, and are 

 likewise beset with strong brown setae, in this respect somewhat resembling B.fusca. 



6. Bairdia crosskeiana, n. sp. (PI. LVII. fig. 10, a-d.) 



Triangular, convex, compressed posteriorly. Left valve large and overlapping the 

 right ; broad, obliquely rounded anteriorly, and tapering to an acute, produced pos- 

 terior extremity ; highest at anterior third. The anterior border is armed with several 

 short, pointed tubercles or spines ; the posterior is acutely pointed, and has a squamous 

 lamina, which is continued along the posterior third of the ventral border. Ventral 

 margin convex ; the dorsal margin much elevated at its anterior third, from which it 

 slopes steeply to the posterior extremity. The right valve is smaller, its dorsal margin 

 truncated in the middle ; anterior extremity broad, obliquely convex, and denticulate ; 

 posterior extremity beaked ; ventral margin slightly sinuated. Viewed from below, the 

 carapace is hastate in outline, very acute posteriorly, and broadest at its anterior third. 

 Surface of the valves smooth, finely punctate. Lucid spots as in B. subdelioidea. 



Length -^ in. (1 mm.)- 



Hab. Levant (sponge-sand). 



Well characterized by the hastate outline as seen from above, the greatly produced 

 tapering hinder extremity, and the spinous anterior border. There are, however, some 

 forms of Bairdia subdelioidea, from Australia, which closely approach it ; and it is a 

 matter of the greatest difficulty to determine the real limits of the various species. 

 My impression is, that the most correct and natural arrangement would be to retain 

 the present B. subdelioidea as the typical form of the species, classing under it, as mere 

 local varieties, B. amygdaloides, B. crosskeiana, and possibly some of the fossil species 

 described by Continental authors. 



Genus Cytherideis, Jones (subgenus). 

 Animal a Cy there. Carapace oblong-oval, reniforra, or subtriangular. " Hinge-mar- 

 gin simple, except that, the central portion of the dorsal margin of the left valve being 

 somewhat incurved under that of the right valve, the anterior and posterior angles of 

 the dorsal margin of the left valve remain somewhat projecting, and present internal 

 shallow furrows for the reception of the corresponding angles of the opposite valve : 

 ventral margin partially incurved." 



1. Cytherideis decora, n. sp. (PI. LVIL fig. 13, a-c.) 



Carapace elongated, triangular, slightly narrowed posteriorly, and highest in the 

 middle. Both extremities rounded, the posterior somewhat produced. The dorsal 

 margin is arched and rather flattened ; ventral margin slightly arcuate. Seen from 



