PllOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 409 



Suborder PROTEOBRANCHIATA. 

 Aimnal with external braiichite. Embryouic shell coni«al. 



Family ACM^ID^. 

 Gill plumose, cervical. 



Geuas Scutellina Gray. 



Scntelliim Gray, P. Z. S. 1847, p. 1G3 =,ScuteUa Broderip, not Lamarck. Type S. crenu- 

 lata Broderip. 



The animal of the typical species of Scutellma is unknown; according 

 to Arthur Adams, that of a closely-allied species {8. ferruginca) resem- 

 bles Acmwa in its externals, except that the shell is pure white, with 

 l^rominently reticulated sculpture, and the apex is prominent, pointed, 

 and very anteriorly situated. Mr. Adams distinctly states that the 

 animal has eyes, and it is quite probable that the genus will eventually 

 lirove to be a good one. 



A specimen was recently obtained, with the dried animal (from some 

 West Indian corals), of a species which is also represented in the Blake 

 collection, and which would probably be referred, from the shell charac- 

 ters alone, to Scutellina, though it ditiers from the received diagnosis of 

 that genus in having a blunt, subcentral, erect apex, much like ordinary 

 AcmiEas. An examination of the soft parts showed, however, wide 

 differences from any described genus, necessitating the establishment 

 of a new one for its reception. 



Genus Pectinodonta Dall. 



Shell resembling Scutellina, with a blunt, subcentral apex. Soft 

 parts resembling Acmcca, except in the following details: Animal blind, 

 with the front part of the head between the tentacles and above the 

 muzzle much produced upward and forward, extending considerably 

 further forward than the end of the muzzle. Muzzle marginated, with 

 lappets at the outer corners. Jaw thin, translucent. Gill exactly as in 

 Acmcva; sides of foot and mantle-edge simj^le, nearly smooth. Denti- 

 tion ^^-^ • teeth large, with transverse pectinated or denticulate 



cusps, lilvc those of the large lateral teeth of some Tcctibrauchs or 

 Nudi branch s. 



Pectinodonta arcuata n. s. 



Shell white, elongate-ovate, moderately elevated, with a blunt, pol- 

 ished apex, on which in young specimens remain traces of the disk-like, 

 chalky, embryonic shell ; the slopes from the apex to the ends both con- 

 vexly arched, margin simple or slightlj^ denticulated by the radiating 

 sculpture; within i)olished; scars as in Acma'a; epidermis none; sculj)- 



