160 MAZATLAN BIVALVES 



Bay : oceasioually found near Boston, and also at Prince Ed- 

 ward's Isl., St. Lawrence " : (? = 0. Canadensis, Lam.*) Conrad 

 quotes it as fossil in Maryland and as common to tke 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- 

 giuica by Sir AV. C. Trevelyan, who also states that the young 

 is the G-rypha^a 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 erperienced naturalists, to 

 confirm this opinion. The species is also from the Portugal 

 Coast iu the Bristol Mus. ; and specimens which appear exactly 

 like those from ? Honduras are in the Br. IMus. from China, 

 on the authority of Tradescant Lay, Esq. The form is also 

 from Australia ; ]\Ius. Cuming. The Mazatlan shells Avhen 

 adult are generally rather incurved, thin, with the attached 

 valve convex, foliated, and undulated with very indistinct 

 radiating furrows, which do not appear at all on the flat upper 

 valve. Cartilage area in the lower valve long, deeply imdu- 

 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. AVhen young, sometimes 

 shaped like the adult, sometimes very broad and sin'eading 

 lieyoud the inner margin, as though in search of a firm founda- 

 tion for future prolongation. The umbo is then often sub- 

 si)iral. 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 iu almost every s])ecimen 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 ; anotlier, not so long within, has a straight 

 area measuring 'SI. The largest specimen in Mr. Darbishire's 

 collection, measures lonff. 9'5, lat. 2'1. 



Ifalj. — Bay of Guayaquil ; in brackish water on mud banks ; 

 Cuming. — Mazatlan ; very rare ; L'pool ij' Havre Coll. — 

 [For localities in other seas, and fossil, v. supra.'] 



* Lamarck's O. Virsinica is cliarncterized by a violet stain on the rauscalar 

 impression ; but Desh. states that the specimens ticketed in his own hand writ- 

 ing have the impression white, while iu his O. Canadensis it is violet. 



