310 



EXPLANATION OF THE NEW PLATES. 



Order. Sessile Cirripedes. 



489. Pyrgoma monticularia. Sab genus, Daracia, Gray, back 



and front. 



490. The same, in situ. 



Fam. Myaria. 



491. Lyonsia Norvegica. Anatina, Nonnul. Inside view of both 



valves. 



492. Outside, with the valves closed. 



493. Naera longirostrum. Anatina longirostris, Lam. Inside of 



both valves. 



494. Outside, with both valves closed. 



495. A smaller species of Nasra, shewing the inequality of the 



valves. 



Fam. Mactracea. 



496. Amphidesma tennis. Abra, Leach. 



497. Ervillia nitens. 



Fam. Corbulacea. 



498. Potamomya, of some authors. A fresh-water shell resembling 



Corbula. Outside, valves closed. 



499. Inside of both valves. 



Fluviatile Conchacea. 



500. Cyclas amnica. Pera, Leach. 



Fam. Cardiacea. 



501. Cardilia semisulcata. Isocardia semisulcata, Lam. Internal 



view. 



502. External view of the same valve. 



503. Cardium apertum. Papyridea, Sw. 



