98 BULLETIN 60, UNITED STATES NATIONAL MUSEUM. 



gin is nearly straight, the carinal margin a little concave, the apex 

 obtuse, truncated. A groove runs near and parallel to the occludent 

 margin, terminating in a notch wliich receives the apex of the scutum. 



The carina is very long, reaching nearly to the apex of the tergum. 

 It is well arched throughout, and near the base is very strongly curved 

 in, extending more than half wa}^ across the base of the capitulum, ter- 

 minating in a slight expansion of the sides, partially .clasping the 

 peduncle, but not forked. The roof is slightly iiattened in the upper 

 part. The sides are wide in the lower two-thirds, tapering near the 

 apex. 



The peduncle is very short. 



Length of capitulum, 5; breadth 2.25 mm.; length of the carina, 

 4.7 mm.; length of peduncle, 0.7 mm. 



This species is related to the west Atlantic O. anierlcanum^ but dif- 

 fers in the shape of the scutum and the narrow, somewhat convex 

 roof of the carina. Like other free-living species, it has the valves 

 better developed than most of the forms living on the gills of crabs. 



Nine specimens examined, the tj^pe lot of four individuals, the 

 largest with capitulum 6.5 mm. long; one 5 mm. long and a very 

 young one from Station 3810; and two of about equal size — capitulum 

 4.5, peduncle about 1.2 mm. long, from Station 4081. 



A new description of a specimen from Station 3810 is given, the 

 station number of the lot originally described having been lost, and 

 the exact localit}^ therefore unknown. 



Plates varying from live, much reduced, to none; when present the 

 umbones of scutum and carina are median or above the middle. 



This group includes the genera Conchoderma^ Ileteralepas^ Alepas^ 

 Anelasma and Chsetolepas. From the shape of the vestigeal scutum 

 and carina and the position of their umbones, it seems likely that the 

 unknown fully armored progenitors of these nude or nearly nude 

 forms were quite unlike Lepas^ Pwcilasvia^ or other allied pentaspidian 

 genera. The cirri have spines arranged in a single continuous or 

 interrupted whorl on each segment in Alepati and Ileteralcpas, but in 

 Concliodernia the spines stand comb-like along the anterior side, as in 

 ScalpeUun^ etc. The taxonomic value of this character remains to be 

 determined. It has not j'et. received careful study in any large series 

 of species. 



Genus CONCHODERMA Olfers. 



1814. Concliodernia Olfers, Der Gesellschaft iiaturforschender Freunde zu Berlin, 

 Magazin fiir die neuesten Entdeckungen in der gesammten Naturkunde, 

 Jahrg. Vlir, drittes Quartal, 1814, p. 177, first species C. virgatum. 



Olion of sonic authors. 



