94 



BULLETIN 60, UNITED STATES NATIONAL MUSEUM. 



umbones of the plates are situated as in Poecilasrna. The typical forms 

 {Octolasmis s. str., including Paradolepas and Trichelaspis) are fragile 

 creatures mainly living as commensals on the gills of crabs or macrura, 

 or on the walls of the gill cavity. They have the calcified portions of 

 the valv^es much reduced, and the base of the slender carina is forked. 

 Another series of species, such as O. orthogonia, sessile^ amerlcanum^ 

 and hawaiense have more strongl}^ calcified valves, the tergum more 

 normally shaped, and the carina expanded into a disk at the base. 

 These may retain the subgeneric name Dichelaspls, type orthogonia. 

 They live externally on crabs, etc. 



KEY TO NORTH AMEKICAX SPECIES OK OCTOLASMIS. 



a. Carina slender, distinctly forked at the base; tergum small, irregular. Living 

 in the gill cavities of decapod crustaceans. 

 b. Scutum composed of a narrow occludent and a wide triangular lateral segment, 

 separated by a rather narrow slit. Antilles, on Palinurus giWs. 0. hoekiSteh- 

 bing. 0. antiguiv Stebbing. 

 hb. Upper margin of lateral segment of scutum at a right angle with the occlu- 

 dent segment. 



Fig. 32.— o, h, Octolasmis gekyonophila. c, O. mClleri. </, o, forresti. x 8. 



c. Lateral branch of scutum rather wide, somewhat triangular and short, not more 



than half the length of the occludent branch; on crabs O.geryonoplnlu. 



cc. Lateral branch of scutum very narrow and nearly as long as the occludent 

 branch. 



d. Scutum. composed of two branches; on crabs 0. mi'dleri. 



d'J. Scutum composed of three slender branches; on Palinurus 0. forresti. 



aa. Carina stronger, expanded in a sort of collar at the base, partiallj' clasping the 

 peduncle; tergum triangular; living externally. 

 b. Scutum L-shaped, with a short lateral segment <J. amcricanum. 



OCTOLASMIS GERYONOPHILA. new species. 



Ti/pe.—C-dt. No. 9038, U.S.N.M. 



Type-localities. — Albatross stations 2215 and 2216." 



« The specimens from these two stations were not kept separate in the collection. 



