V %9 h '] PROCEEDINGS OF THE NATIONAL MUSEUM. 289 



modify. This classification, augmented by the new discoveries of the 

 past three years, may be expressed in brief as follows: 



Family Cuspidariida". abranchiate, siphoseptate, septum foramirtate. 

 Genus Cuspidaria (etc.) with long siphons; oral palpi obsolete. 

 Genus Myonera, short siphons; oral palpi absent. 

 Family Poromyidce: septibranchiate, siphoseptate. 



Genus Poromya : teeth strong; oral palpi large; foramina of septum slit-like, be- 

 tween the close-set lamellae arranged in two interrupted longitudinal series; 

 pallial sinus obsolete ; surface of shell granular. 

 Subgenus Dermatomya : shell not granular; pallial sinus developed; hinge 



strong. 

 Subgenus Cetomya : shell granulous ; pallial sinus obsolete; hinge teeth ob- 

 solete in the adult. 

 Genus Cetoconcha : hinge teeth, obsolete in the adult; pallial sinus obsolete; 

 siphoseptum foraminate, the foramina arranged in four longitudinal series, 

 solitary, the subtubular lips filling the office of gills. 

 Family Verticordiidce: siphoseptate with small adnate ctenidia; oral palpi almost ob- 

 solete; septum imperforate. 



Lyonsia and probably Lyonsiella may be called branchioseptate, and 

 should be referred elsewhere. 



Genus POROMYA Forbes. 



Poromya cymata sp. now 



Plate vm, Fig. 4. 



Shell small, ovate, inequivalve, the right valve most inflated and 

 larger; hinge of the normal Poromya like P. granulata ; umbo in the 

 right valve high, inflated, prominent; anterior end rounded; posterior 

 end with a narrow, sharp keel radiating from the umbo between two 

 shallow, wide, gently excavated furrows which undulate the margin; 

 surface covered with rather sparsely set granules, coarser toward the 

 margin, finer on the umbo and posterior waves and disposed in radiat- 

 ing lines; left valve (as in Corbula) proportionately longer and less high 

 and with deeper excavations where the furrows come to the margin; 

 the furrows are also wider and extend further forward on the valve, 

 which is less inflated than the right valve; the granulations, too, seem 

 more close set and a little more irregular; there is no lunule or es- 

 cutcheon; the epidermis is pale yellowish, under which the surface 

 seems iridescent; the interior is brilliantly pearly; the muscular scars 

 are faint, the pallial line simple, with some flexuosity near the posterior 

 scar, but too irregular to be termed a sinus; the whole interior shows 

 indications of radiating stri oe which appear as marked grooves or crenu- 

 lations on the basal margin of the valves. Eight valve, altitude 10; 

 longitude 9; diameter 3.5 mm . Left valve, altitude S.~>; longitude 11; 

 diameter 3 mra . These valves are not pairs. 



Hab.— At U. S. Fish Commission Station 2762, east of Rio Janeiro, 

 in 59 fathoms, mud bottom ; temperature 57°.l F. 

 Proc. N. M. 89 19 



