54 THE VOYAGE OF H.M.S. CHALLENGER. 



Adriatic on the gills of Maya squinado. However, there can be little doubt but this is 

 indeed a species of Dichrfaspis, and I even feel convinced that it is the same as 

 Dichchispis danrinii, Filippi. 1 Conchoderma coronularium I have not been able to 

 make out ; whether it corresponds to Conchoderma auritum, Linn, sp., or perhaps repre- 

 sents a different species, I cannot say. Perhaps it is the same as Otion stimpsoni, Dall, 

 which species is founded upon a very imperfect description without figures by Mr. Dall. 2 

 This species has, according to this author, only the scuta, whereas typical specimens (accord- 

 ing to Leach, and also according to Darwin) are furnished with five valves (two scuta, 

 two terga, and a carina). Darwin says, however, that in Conchoderma auritum the terga 

 and the carina are often absent, and this seems especially to be the case in the large 

 specimens which are found attached to Coromdce on whales. Now, the specimens which 

 Mr. Dall took from Coronxda (sessile on the " Humpback ") had a length of almost 5 

 inches (peduncle 2 '8 inch, body 2*16 inch); I therefore think it very probable that the 

 species of Mr. Dall is the same as Conchoderma auritum. which, according to Mr. Darwin, 

 is a world-wide and extremely common species. 



The characters of the genus are the following : — Capitulum almost totally mem- 

 branous ; valves two to five, minute, remote from each other ; scuta with two or 

 three lobes, with their umbones in the middle of the occludent margin ; carina arched, 

 upper and lower ends nearly alike. Filaments 3 numerous, not only two pairs seated 

 beneath the basal articulations of the first pair of cirri, but also on four or five anterior 

 pairs; mandibles with five teeth, finely pectinated ; maxillae with distinct steps; caudal 

 appendages none. 



No fossil remains of this genus are known. The smallness of the calcified valves may 

 possibly be the cause of this ; it would be rather rash in my opinion to conclude that 

 it is a genus of recent occurrence only, because it has not as yet been found in fossil 

 deposits 



Both species are extremely common, and have, as Darwin says, a world wide distribution. 

 They live attached to floating objects, bottoms of ships, sea-weed, turtles, whales, &c. 

 They can be distinguished from each other in the following way : — 



1 Of this species Heller gives the following description: — " Stiel vom Kopfchen deutlich abgesetzt, his 2A'" lang, 

 das Kopfchen von fast gleicher Lange, umgekekrt herzformig, hinten hreit, nach vorn und unten verschmalert. Der 

 Mantel ist diinn, halhdurchsichtig, gelblichweiss, nur durch einige kleine Kalkreifen gestiitzt. Die Carina erscheint 

 ehr diinn, verlauft am obern stark gekriimmten Rande nach hinten, wo sie sich in zwei Schenkel theilt, die beiden 

 Bchmalen Scuta sind ebenfalls zweischenkelig, die Schenkel unter eineni zicmlich spitzen Winkel vereinigt. Auch finden 

 sich nach vorn hin zwei kleine hakig gekriimmte Tergalstiicke in der Mantelhaut. Der Korper selbst ist am Vorderende 

 in ein hakig gekrummtes Rostrum verliingert. 



! Proc. Calif. Acad. Nat. Uci., vol. iv. 1873, p. 301. 



3 Gerstacker (Joe. cit., p. 535), calls the filaments of Conchoderma filamentary gills (geisselartige Kiemen). I do not 

 believe, however, that it is proved that these structures are respiratory. 



