GASTEROPODA. 377 
CREPIDULA NuMMARIA (Gould). 
Testa tenuis, explanata, circularis, alba, strits incrementalibus laxis in- 
sculpta, epidermide flavo-cornea induta ; apice viz conspicuo, margr- 
nali: septum internum latius quam longum, deorsum fornicatum ; 
margine flexuoso: cavositas feré nulla. 
Crepidula nummaria, Goutp ; Proceed. Boston Soc. Nat. Hist., i. 
160. August 1846. Expedition Shells, 15. 
Suet thin, white, circular, and perfectly flat, externally wrinkled 
by the loose stages of growth, and covered by a thick, yellowish epi- 
dermis. The apex is marginal and scarcely visible. The internal 
lamella is broader than long, arching, so as to enlarge the cavity which 
would otherwise be almost nothing. Its edge is flexuous, retreating 
near the middle. 
Diameter three-fourths of an inch. 
Obtained at Classet, Straits of De Fuca, Oregon. 
This very peculiar shell is well characterized by its perfectly flat, 
circular form. It probably grew within some other shell, and other 
specimens may be found moulded into a different form. It is sepa- 
rated from C. lingulata by the form of its septum. 
Figures 480, 480 a, 480, superior, inferior, and lateral views of the 
shell. 
CrepiwuLa costata (Desuayes), in Lamarck, Anim. sans. Vert., 
vii. 644. Quoy and Gammarp; Voy. de l’Astrol., pl. 72, f. 10-12. 
ANIMAL with the foot colourless, linguiform, short; mantle greenish- 
yellow, shaded and edged with azure; head small, distinct, bilobate ; 
tentacles subulate, with the eyes near the external base. 
95 
