132 ARMSIA. 



tral Pacific Islands," and neither has been figured or seen 

 by any subsequent author. Mr. Sykes did not find them in 

 the British Museum collection ; they are not in the collections 

 at Philadelphia or Washington, nor is any trace of them to 

 be found in the Pease collection at Cambridge, Massachusetts. 

 We learn from labels in the Academy collection that Andrew 

 Garrett knew them not. It must be admitted that the diag- 

 noses are insufficient for positive identification; and in the 

 absence of types, the names may be regarded as defunct. 



P. prostrata Pease. 



"Shell thin, depressed, deeply umbilicate, greenish-cor- 

 neous, decussated with close and very fine striae. Whorls 4, 

 flat, rapidly increasing, the last wider, acutely angular, 

 grooved near the margin above, dilated in front, convex be- 

 neath, apex depressed. Aperture widely rotund-lunar; per- 

 istome simple, acute. Alt. 2*4, diam. 6 mm." (Pse.) 



Islands of the central Pacific (Pease) ; Lanai? (Pease). 



Helix prostrata PSE., P. Zool. Soc. 1864, p. 670, no. 9; 

 P. Z. S. 1871, p. 475. 



Genus ARMSIA, n. gen. 



Amastrina with the shape of Gonyodiscus, very broadly 

 umbilicate, the embryonic whorls convex, projecting, and 

 spirally striate, the peristome well expanded, thin, and with- 

 out a columellar lamella. Type A. petasus. 



This group differs from all forms of Pterodiscus and Plana- 

 mastra by the decided convexity of the projecting embryonic 

 whorls and the stronger expansion of the peristome. Like 

 Planamastra it lacks trace of a columellar lamella. I have 

 not seen the embryo except as exposed in grown shells, but it 

 must differ markedly from that of Pterodiscus and Plana- 

 mastra. The embryonic whorls are worn in the shells exam- 

 ined, but in places they show rather coarse spiral striae, which 

 are wanting on the radially costate later whorls (pi. 25, fig. 

 7) . The soft anatomy is unknown. It is probably vivi- 

 parous, like the related genera. 



While evidently related to Planamastra, Armsia has 



