414 PROCEEDINGS OF THE ACADEMY OF [Sept., 



related, M. minus antl M. helium differ in many details of structure, the 

 scuta, carina, cirri and mandibles all being diverse in the two forms, 

 which must be held specifically distinct. M. striahmi Hoek is related 

 to M. helium by the cirri and mandibles, but differs in the terga and 

 the sculpture of the bases of scuta and carina, etc. It differs from M.- 

 ininus by the same characters of the plates, and also by the armature of 

 the cirri and to some extent in the mandil)les. 



MeGALASMA GR AGILE AND M. GRACILIUS. 



Megalasma gracile (Hoek) was originally described (as Pcccilasma 

 gracile) from a Challenger station off Sydney, New South Wales. I have 

 elsewhere called attention to the doubt attaching to material from this 

 station, owing to the mixture therein of molluscan species otherwise 

 kno^^'n only from the Atlantic, with others known to be Australian.** 

 That Megalasma gracile was really from the Australian station is 

 rendered more probable by the discovery of several specimens in the 

 Indian Ocean by the Indian Marine Survey, as recorded by Dr. Annan- 

 dale.^ The western Atlantic M. g. gracilius may prove to be identical 

 with Hoek's form, yet in view of the wide geographic separation, and 

 of several minor differences in the plates, I have thought best to 

 segregate it as a subspecies. This course is likely to prove less injuri- 

 ous to science than an inconsiderate lumping of forms from widely 

 separated areas, without actual comparison of specimens. Dr. Ploek 

 has written well on this topic. *° 



The cirri of M. gracilius differ somewhat from those of M. gracile as 

 described l3y Hoek.^^ He states that the posterior pair of cirri have 

 segments "bearing as a rule four pairs of spines, the lowest pair of 

 which is very minute, the second pair minute." 



In M. gracilius the posterior cirri have five or six pairs of spines, the 

 lower pair minute, on the 6th to 10th segments; beyond that point 

 there are four pairs, then decreasing to three, and finally one or two on 

 the outermost segments. Cirri iii to vi are practically alike. Cirrus ii 

 has many additional spines, partly disposed in a row parallel to that on 

 the anterior border, partly arising along the distal border of each seg- 

 ment. The inner ramus is mucli the longer, comi)osed of 15 segments,, 

 the outer having 13 segments. 



** Bull. U. S. Nat. Mus., \o. 60, p. S9. 

 ^ Rexords of the Indian Mufieum, I, pt. 1, p. <S1, 

 '" ChaUengcr Report, VIII, Cirripedia, p. 145. 

 " CJiidlfiKjtr Report, Cirripedia, p. 47. 



