204 



POST-TERTIARY ENTOMOSTRACA. 



as seen from above, subsagittate, widest behind the middle, width equal to nearly 

 two thirds of the length ; anterior extremity pointed, lateral margins sloping in a 

 curved line outwards to near the posterior third, where they sink suddenly, forming a 

 rectangular projection, the hinder third of the shell constituting a large triangular process. 

 End-view triangular, the angles all acute. Surface of the shell smooth, bearing more or 

 less numerous scattered circular papillae, and usually with indistinct transverse striato-reti- 

 culate sculpture ; the lateral alse prominent, rounded off gradually in front, rectangular 

 behind, and in old specimens bearing at the angle a strong, awl-shaped mucro or spine. 

 Length, -^th of an inch. 

 At one time we supposed this interesting species to be identical with the Cypridina 

 vespertilio of Reuss and of Egger, but further acquaintance with it and other allied forms 

 convinces us that we were mistaken in that supposition, and that the C. vespertilio of 

 those authors is really referable to an immature stage of Cytheropteron alatum, G. O. 

 Sars.^ Young specimens of C. arcuatum have the lateral alse, as a rule, well rounded, 

 and are destitute of the angular spine ; the shell is also more fully papillated, but the 

 reticulated surface-ornament, on the contrary, seems to become more distinct with age. 

 C. hamatum, of G. 0. Sars, is very nearly allied to the present species, but that author 

 himself, from actual examination, considers it to be distinct, an opinion in which we 

 entirely agree with him. The difference is chiefly that of outline, C. arcuatum being 

 more boldly arched, and with blunter, wider, and less produced extremities ; in these 

 particulars (though in no others) C. hamatum more resembles the C. injlatum of the present 

 Monograph. 



Distribution, Recent. — Baffin's Bay. 



Fossil. — Scotland : Tangyburn, Elie, Dryleys, Errol. Ireland : Woodburn. 



4. Cytheropteron inflatum, 7iov. sp. Plate VIII, figs. 24 — 27 ; Plate XIV, 



figs. 26—29. 



1868. Cytheroptekon ixflatum, B., C, and R. Ann. Mag. N. H., ser. iv, vol. ii, 



p. 33, pi. V, figs. 8—10 (figured 

 but not described). 



Carapace, as seen from the side, subrhomboidal, highest in the middle, height equal to 

 two thirds of the length ; anterior extremity somewhat produced, rounded ; posterior 

 produced into an obtusely rounded median beak; superior margin boldly arched, 

 gibbous ; inferior convex in the middle along the line of the alseform process, slightly 



1 Cytheropteron inornatum, B. and R. (see Ann, and Mag. N. H. (1872), ser. iv, vol. ix, p. 61, pi. ii, 

 figs. 1 — 3), is likewise only a stage of development of C. alatum. We therefore take this opportunity of 

 withdrawing the name. 



