216 UNGULINIDiE. 



projecting from the base of the shell or folded up between the 

 gills ; palpi pointed; gills two on each side, unequal, the external 

 narrower, with a free dorsal border, inner widest in front. 



AxiNOPSis, Sars, 1878. 



Distr.—A. orhwulata, Sars ^cxix, 69, 10). Norway. 



Shell discoidal, tumid in the middle, compressed towards the 

 margins; umbones slightly prominent; no external ligament; 

 valves thin, pellucid, white, concentricall}' striate ; cai'dinal tooth 

 in the right valve obtusely elevated, recurved, in the left valve 

 elongated, subhorizontal ; cartilage narrow. 



Mysia, Leach, 1819 (Brown, 1827). 



Syn, — Diplodonta, Brown, 1831. 



Disfr. — 40 sp. West Indies, Rio, Britain, Mediterranean, Red 

 Sea, West Africa, India, Gorea, Australia, California. Fossil, 

 30 sp. Cretaceous, Eocene — ; United States, Europe. M. Bra- 

 siliensis, Phil, (cxix, 71). 



Shell suborbicuiar, smooth ; ligament double, rather long, sub- 

 marginal ; hinge-teeth 2'2, of which the anterior in the left valve, 

 and posterior in the right are bifid ; muscular impressions pol- 

 ished, antei'ior elongated. 



Animal with the mantle-margins nearh^ plain, united ; pedal 

 opening large, ventral ; foot pointed, hollow ; palpi large, free ; 

 gills two on each side, distinct, the outer oval, inner broadest in 

 front, united behind ; branchial orifice small, simple ; anal larger, 

 with a plain valve. 



TENEA, Conrad, 1870. Shell roundly ovate, thin, tumid ; left 

 valve under the apex with a V-shaped tooth, the anterior lobe of 

 which is continued along the anterior margin of the shell, sepa- 

 rated by a deep groove from it ; in the right valve are two 

 cardinal teeth united above, the anterior is falcate, with a pit on 

 each side, the posterior curved and directed obliquely backwards. 

 M. paiHlis^ Con. (cxix, 72). 



FELANiA, Recluz, 1851. Shell sublenticular, equivalve, equi- 

 lateral, thin, with an epidermis; beaks and lunule small; two 

 divergent subapical teeth, the posterior of the right and anterior 

 of the left valve channeled or bifid ; no lateral teeth, but in place 

 of them a deep, long groove on each side the cardinals ; liga- 

 ment cartilaginous, very long ; muscular impressions oval-oblong ; 

 pallial line with a short trigonal sinus. 10 sp. M. j^osea, Recluz 

 (cxix, 73, 74). 



HipPAGUS, Lea, 1833. 



Distr. — H. Isocardioides, Lea. Eocene ; Ala. 



Shell ovate, higher than long, tumid, with prominent, atten- 

 uated incurved beaks ; of moderate thickness ; internal and 

 external superficial layers of a silky appearance ; hinge edentu- 



