of the North Atlantic and of North-Western Europe. 661 



seems to us, however, that the organs, as figured by Herr Miiller, do not differ, 

 except in the degree of development of their various parts, from those of 

 Philomedes, and tliat other members of the genus, if such deviations were 

 admitted as generically valid, would also require new generic names. This 

 opinion is based, we must admit, solely on a study of Herr Miiller's figures. 

 We, ourselves, have seen only the male, while the peculiarities in question are 

 not found except in the female.] 



5. Philomedes Mac Andrei (Baird). 

 (PL LI., figs. 7, 8 ; PL lii., figs. 5, 6.) 



1848. Cypridina Mac Andrei, . Baird, "Note on the G-enus Cypridina, M. 



Edwards, with a Description of two new 

 species," Ann. & Mag. Nat. Hist., ser. 2, 

 vol. i., p. 21, pi. vi. B, figs. 1, 2. 



1850. „ „ . . Baikd, "Nat. Hist. Brit. Eutom.," p. 179, 



pi. xxii., fig. 1 a—g. 



1868. Bradycinetus Mac Andrei, Beady, G. S., " Mon. recent Ostrac," Trans. 



Linn. Soc, vol. xxvi., p. 468, pi. xxxiii., 

 figs. 14—17 ; pi. xli., figs. a—g. 



Shell subrotund, beyond which general form the rostrate frontal process, and the 

 produced infero-posteal corner form projections ; greatest height central, equal to 

 two-thirds of the length ; ventral margin rather strongly arched throughout its 

 length, but much less tumid than the dorsal ; dorsal margin remarkably, boldly, 

 and continuously arched from the rostrate process right round the posterior 

 extremity until the infero-posteal corner is reached; that corner is produced down- 

 wards into a short, compressed, triangular process, the front margin of which is 

 crenated; anterior rostrate projection consisting of an underlying portion of thin 

 texture (often shrivelling up when the shell is dried), and not unlike in 

 form to the rostrate extremity in P. Lilljeborgii ; overlying this is a raised 

 calcareous portion, which forms, on each side, a horn-like process running out to 

 an acute extremity, and strongly curved outwards and forwards ; antennal sinus 

 narrow, opening downwards, the upper side is slightly convex, and slopes upwards 

 to form the horn-processes, the lower side is slightly convex, and sweeps round 

 without any angularity to unite with the ventral margin ; surface of valves ivory 

 white, glabrous, and highly polished. Seen from above the form is broadly ovate ; 

 anteriorly the points of the rostral process are seen extended laterally like horns 

 on each side, while the infero-posteal processes are projected backwards in 



TEANS. ROT. DUB. SOC, N.S. VOL. V., PAET ill. 5 A 



