169 MAZATLAN BIVALVES 
Bay : occasionally found near Boston, and also at Prince Ed- 
ward’s Isl., St. Lawrence”: (?=O. Canadensis, Lam.*) Conrad 
quotes it as fossil in Maryland and as common to the U. States 
and Europe recent: “Found at Nissau, between Narbonne 
and Beziers in France, teste Brongniart.” A similar shell is 
in the Br. Mus. from Africa. Another specimen, from the 
mouth of the Tagus, with a fossil from Lisbon, are marked 
O. longirostris, Lam. They are considered a var. of O. Vir- 
ginica by Sir W. C. Trevelyan, who also states that the young 
is the Gryphxa angulata of Lam. The type.specimen of the 
latter in the Br. Mus, and the young specimens from Mazatlan, 
appear to me, though not to more experienced naturalists, to 
confirm this opinion. The species is also from the Portugal 
Coast in the Bristol Mus. ; and specimens which appear exactly 
like those from ? Honduras are in the Br. Mus. from China, 
on the authority of Tradescant Lay, Esq. The form is also 
from Australia; Mus. Cuming. The Mazatlan shells when 
adult are generally rather incurved, thin, with the attached 
valve convex, foliated, and undulated with very indistinet 
radiating furrows, which do not appear at all on the flat upper 
valve. Cartilage area in the lower valve long, deeply undu- 
lated, generally pointing to the left, sometimes to the right, or 
straight. Attachment sometimes only to a stick, sometimes to 
shells by a large part of the surface. When young, sometimes 
shaped lke the adult, sometimes very broad and spreading 
beyond the inner margin, as though in search of a firm founda- 
tion for future prolongation. The umbo is then often sub- 
spiral. In this state it may be generally distinguished from 
neighbouring species by the rich sub-nacreous orange and 
violet colouring, and absence of crenations near the hinge. 
Sometimes however it is nearly white, as it generally is when 
adult. The muscular scar is generally kidney-shaped, but 
varies in almost every specimen according to the breadth or 
prolongation. The hinge area is generally hollowed beneath. 
The youngest identified specimen is °93 long, of which °16 is 
spiral ligament-area ; another, not so long within, has a straight, 
area measuring "34. The largest specimen in Mr. Darbishire’s 
collection, measures long. 9°5, lat. 2°1. 
Hab.—Bay of Guayaquil; in brackish water on mud banks ; 
Cuming.—Mazatlan ; very rare; L’pool § Havre Coll.— 
| For localities in other seas, and fossil, v. supra. | 
* Lamarck’s O. Virginica is characterized by a violet stain on the muscular 
impression ; but Desh. states that the specimens ticketed in his own hand writ- 
ing have the impression white, while im his O. Canadensis it is violet. 
