144 ANATINID^. 



pallial line simple. All the species at present known are from 

 North American seas. P. claviculata, Carp. 



Myodora Gray, 1840. 



Bistr. — 12 sp. New Zealand, New South Wales, Philippines. 

 M. striata^ Qiioy (eviii, 50). 



Shell trigonal, rounded in front, attenuated and truncated 

 behind ; right valve convex, left flat ; interior pearly ; cartilage 

 narrow, triangular, between two tooth-like ridges in the left 

 valve, with a free sickle-shaped ossicle ; pallial line sinuated ; 

 structure like Anatina; outer cells large, rather prismatic. 



Myochama, Stutchbury, 1830. 



Bistr. — 5 sp. New South Wales ; attached to Crassatella and 

 Trigonia, in 8 fathoms water ; the fry (as indicated by the um- 

 bones) is free, regular, and Myodora-shaped. 3L anomioides, 

 Stutchb. (cviii, 51-53). M. Keppelliava, A. Ad. (cviii, 54). 



Shell inequivalve, attached by the dextral valve and modified 

 by the form of the surface of attachment ; posterior side attenu- 

 ated ; left valve gibbose ; cartilage internal, between two tooth- 

 like projections in each valve, and furnished with a movable 

 ossicle ; anterior muscular impression curved, posterior rounded, 

 pallial sinus small. 



Animal with mantle-lobes united ; pedal opening and siphon 

 surrounded by separate areas ; siphons distinct, unequal, small, 

 slightly fringed ; a minute fourth orifice close to the base of the 

 branchial siphon ; visceral mass large, foot small and conical ; 

 mouth rather large, upper lip hood-like ; palpi tapering^ few- 

 plaited ; gills one on each side, triangular, plaited, divided by 

 an oblique line into two portions ; excurrent channels four, two 

 at the base of the gills and two below the dorsal laminse. 



( Tlii^acise.) 



AsTHENOTHiERUS, Carpenter, 1864. 

 Bistr. — A. villosior^ Carp. Cape St. Lucas, L. Cal. 

 Shell like Thracia, hinge without teeth, spongy cartilage situ- 

 ated in a pit under the umbones. 



Thracia (Leach), Blainville, 1824. 



Syn. — Odoncinetus, Costa. Cinctodonta, Herm. Corymya, 

 Agassiz. 



Bistr. — 2t sp. Greenland, United States, Norway, Britain, 

 Mediterranean, Canaries, China, Sooloo; 4-110 fathoms. Fossil, 

 36 sp. (Trias?) Lower Oolite — ; United States, Australia, 

 Europe. T. piibescens, Pult. (cviii, 55). T. plicata^ Desh. 

 (cviii, 56). 



