1007.] XATfUAL SCIENCES OF PIIILADELPIIIA. 415 



The inaudible of M. (iniciliu.s is similar to lloek's liu\n-e of that of M . 

 <iracilc. the lower point being minutely iMfiil. 



Key to Species of Megalasma. 



a. — Pc;huicular margins of scutum and carina continuous with the 

 occludent margin, in the same direction, the umlxj of the scutimi 

 therefore aliove the basal angle of the plate. Indo-Pacific 



province, {Megalasma s. sir). 



b. — A pedimcular area on each side defined by a semicircular 

 ridge on the bases of scutum and carina; roof of the carina 

 very wide; width of scutum about two-thirds its length; 

 tergum triangular, the occludent margin about half the 

 length of the scutal. rapituluni 11 mm. long. Phili))pine 



Archipelago ^1/. striatum Irloek. 



h'. — Peduncular area defined by a semicircular groove; width of 

 scutum slightly more than half its length; tergum cjuad- 

 rangular, the occludent margin about one-fourth as long 

 as the scutal margin. Capitulum 6.5 mm. long. Indian 



Ocean M. carinodcntatum Weltner. 



h" . — Xo distinctly defined pedimcular area on the liases of scuta 

 and carina; scutum nearly twice as long as wide; occludent 

 margin of terg\un about one-third the length of the scutal 

 margin. 

 c. — Basal margin of carina straight with a rounded median 

 projection, the sides narrower than in P. helium; 

 lateral margins of the peduncular orifice arched for- 

 ward. Capitulum 6.5 to mm. long. Segments of the 

 cirri w4th 3 pairs of large spines, 1 pair of ver}' small 

 ones. Andaman Sea, . . M. minus Annandale. 



c'. — Basal margin of carina convex, deeply arched, the sides 

 wide; lateral l)orders of the peduncular orifice straight. 

 Capitulum 12 to 15 mm. long. Segments of cirri with 

 4 pairs of long spines, 1 pair of small ones. Hawaiian 



Islands, M. helium Pilsbry. 



a'. — Peduncular or basal margin of scutum making about a right angle 

 with the occludent margin, the umbo of the scutmn at the baso- 

 ventral angle of the plate. . (subgenus Glyptelasma Pilsbry). 

 h. — Umbo of the carina projecting beak-like behnv the base of the 

 scutum, and making an angle with it. 

 c. — Basal margin of carina as long as the basal margin of the 

 scutum; internal basal plate long, lozenge-shaped; 

 sides wide in the lower half. 

 d. — Peduncle about one-third the length of the capitulum ; 

 basal margin of scutum half the width of carina 

 near its base. Capitulum 7 nun. long. Off Aus- 

 tralia; Indian Ocean. . . . .1/. f/raci/c Hoek. 



