280 BULLETIN OF THE 
Famity POROMYID Dat. 
Gexus POROMYA Forpes. 
Poromya Forbes, 1844; Embla Loven, 1846. Type P. anatinoides Fbs. (= P. granu- 
lata Nyst.) 
Shell gaping a little behind, granulose externally under a thin epidermis, in- 
ternally with an internal cartilage in a stout posteriorly directed fossette over 
which a linear external ligament extends from under the beaks backward over 
the cartilage to the posterior end of the hinge-line; before the cartilage in the 
right valve is a stout cardinal tooth, generally notched in front; in the left 
valve is a small sunken triangular tooth in front of the fossette, and a long 
distant posterior lateral tooth lies behind the beak. There is a very slight 
indentation of the pallial line, the foot is long and cylindrical, the siphons 
rather short, surrounded with a fringe of rather stout tentacles. There is no 
ossicle. Gills as in Cetoconcha, with no free branchie. ‘The interior of the 
shell is faintly pearly under a wash of non-perlaceous substance. 
Section CETOCONCHA Datu. 
Shell differing from Poromya proper by the cartilage being almost external 
and the fossettes diminished in size and upturned, the external ligament con- 
sequently nearly obsolete ; the dentition obsolete except the cardinal tooth of 
the right valve, which itself is sometimes absent in the adult, though observ- 
able in the young shells; other shell characters much as in Poromya. The foot 
is compressed and hatchet-shaped, grooved behind; the mouth has two large 
superior palpi and two (or none) small inferior palpi not modified as gills. 
The foot stands ina socket as in Verticordia and Cuspidaria. On the ventral 
surface of the body, behind the foot, are two (sometimes four) rows of less than 
semicircular lamella closely adjacent to each other and firmly fixed to the sur- 
face by the whole base of each lamina. There is one row on each side with a 
shorter supplementary outer row in other cases. They radiate forward in a 
curve from a point a little distance behind the foot, and may quite or not quite 
meet at this point. In C. elongata I found no inferior palpi, a state of things 
perhaps due to injury, though the specimen seemed perfectly preserved; the 
other species had them. In all there was a row of similar lamelle to those 
above described, starting on each side from behind or under the inferior palpus 
of that side, or the place in front of which it should have been, and extending 
backward in such a curve as would, if prolonged, have joined its posterior end 
to the anterior end of the row coming from behind the foot. The lamell are 
not connected by a raphe. These lamelle represent the branchiz of ordinary 
Pelecypods, and if even these are absent, as seems possible, in Cuspidaria, it 
is difficult to doubt that we have a progressive series: in Cuspidaria none; in 
