igog.] N. AnnandaIvE : The Indian Cirripedia Pedunculata. 97 



from the occludent. Scutum not much inflated, its vertical length about six times 

 the length of the occludent margin of the tergum ; external surface bearing a single 

 well-marked semicircular ridge, which extends from near the umbo on the occludent 

 margin to the point where the carina, tergum and scutum meet; a strong umbonal 

 tooth on both scuta. 



Pedunci^e relatively stout, very short. 



Cirri, etc. — -First cirrus widely separated from second; its anterior ramus reaching 

 the distal extremity of the penultimate joint of the posterior ramus; rami with 

 eight or nine joints, slender with both margins spinose. Other cirri normal, with well- 

 developed anterior fringes and posterior bunches of bristles ; the number of bristles 

 in each of the latter being variable. Anal appendages short, uniarticulate, truncated, 

 bearing a row of short bristles at the tip. Penis moderately long, slender, bearing 

 numerous fine scattered hairs on its surface and a somewhat less sparse bunch of 

 similar hairs at the tip. 



Mouth parts somewhat variable, as in most species of Pœcilasma and Mega- 

 lasma. Lahr urn bullate, with a row of small triangular teeth. Maxilla with the biting 

 edge forming a ^-like outline, the excavation being deep and rounded and having its 

 inner margin with a curved and gradual slope; three stout spines external to the 

 excavation, several fine hairs at its base and about twelve slender spines on its inner 

 margin and internal to it. Mandible with four or five teeth, the innermost tooth, when 

 five are present, being narrow and spine-like; the greater part of the mandible covered 

 with minute bristles arranged in small transverse rows of three or four bristles each. 



This species is common in the deeper parts of the Bay of Bengal and has recently 

 been found in the Malay Archipelago. Pilsbry has described a very similar form 

 from the S. Pacific under the name Pœcilasma helium ^ and later ' has published an 

 elaborate comparison between this species and Megalasma minus. Undoubtedly 

 differences exist between these two forms, and I find that most, though not all, of 

 the differences noted by Pilsbry are constant. Moreover, I owe to his kindness the 

 opportunity of examining a specimen of M. helium. I do not think, however, that the 

 two forms should be regarded as specifically distinct, for they seem to me to be 

 merely local races, differing from one another in minute and comparatively unim- 

 portant characters. The following table will serve to distinguish them from one 

 another, but I should not be surprised to find that other "species" in the genus 

 should (if my views as to what constitutes a subspecies be correct) be regarded as sub- 

 species of M. minus. 



Megalasma minus. 



Race I (typical form). — Vertical length of scutum at least twice the greatest 



transverse diameter. 

 Race II {Megalasma helium, Pilsbry). ^Vertical length of scutum less than twice 



the greatest transverse diameter. 



' Bull. Bur. Fisheries, xxvi, p. 183, pi. iv, fig. 6 (Washington, 1907). 



* Proc. Acad. Nat. Sei. Philadelphia, lix, p. 409 (1907). The first paper was written some time 

 before publication. 



