THE BAENACLES IN THE U. S. NATIONAL MUSEUM. 87 



convex. The size of adult examples is also subject to considerable 

 variation. 



P. inseqiiilaterale is closely related to P. ksempferl^ but it differs by 

 the decidedly smaller tergum, less arcuate occludent border and fre- 

 quently more asymmetrical valves, though some individuals are nearly 

 equivalve. P. crassum is a shorter, wider form, with the occludent 

 border more strongly arched, and having a well-developed embedded 

 appendage at the umbonal end of the carina, wanting in I*, insequi- 

 laUrale. 



There is great variation in the degree of asymmetrj^ among the spec- 

 imens from most stations. Either the right or the left valve may be 

 the more convex. Figs. 6, 7, 11, and 12 represents individuals of the 

 t3^pe lot, figs. 6 and 7 being the type. The interior, fig. 8, is drawn 

 from specimens taken off Key West, Florida, in 70 to 80 fathoms, on 

 Scyramafltki cranfin A. Milne-Edwards. 



PGECILASMA IN/EQUILATERALE BREVE, new subspecies. 



Plate VI, figs. 9, 10. 



Type.—Q^i. No. 82919, U.S.N.M. 



Type-locality. — Albatross Station 2352, Gulf of Mexico, north lati- 

 tude 22° 35', west longitude 84° 23', in 463 fathoms, on Bathyplax 

 typJila A. Milne-Edwards. 



Similar to P. inseqiiilaterale., but the capitulum is very short and 

 broad, and the tergum is much reduced. It differs from P. erassuvi 

 by the straight occludent border of the scutum. 



Length of the capitulum 7.5, breadth 5.3, diameter 3 mm. 



Only two specimens were taken. 



Genus MEGALASMA Hoek. 



1883. Megalasmn Hoek, Challenger Report, Zoology, VIII, p. 50. Type, M. 

 sfriatiun . 



. This genus differs from P(xcilasm.a in the shape of the carina, which 

 is enlarged at the sides toward the base, with a concave plate inside, 

 terminating upward in two stout teeth. The peduncle is very short. 

 So far as 1 know, they do not live on crabs. The relationships of the 

 group are discussed under Pmcilasma. 



Subgenus GLYPTELASMA Pilsbry, new subgenus. 



The type of this group is M. suhcarinatum. These barnacles live 

 chiefly on sea-urchin spines, on the larger forms of Scalpellv?n, etc.. 

 not, so far as I know, on crabs. The peduncle is quite short, not so 

 long as in typical Pcecilasma. 



