236 TESTACEOUS MOLLUSCA. 



narrow and seemingly curved upward, from the sudden obliquity 

 of the centrally incurved ventral edge; anterior edge long, scarcely 

 at all retuse, extremity produced, attenuated, rounded ; dorsal angle 

 distinct, compressed; within purple anteriorly. \\..2\. — South 

 America.? 



M. Sordida. Nobis. Z. P. 1844. Oblong, ventricose covered 

 with an olive green epidermis, and anteriorly with a lamellar mem- 

 branaceous yellowish-ashy covering, which is here and there pro- 

 duced into lanceolate spines ; hinge margin rather short, but 

 slightly elevated, the dorsal angle very obtuse ; anterior edge 

 elongated, (in the adult, retuse) extremity obtuse ; ventral edge 

 strongly incurved ; umbonal ridge prominent, edged posteriorly 

 with a paler ray ; posterior extremity extremely short and obtuse ; 

 within tinged anteriorly with purple. lj..2f. — General shape of 

 M. Modiolus. 



M. Arcuatula Nobis Z. P. 1844. Narrow, elongated, subar- 

 cuated, compresssd, smooth, very fragile, under a greenish fulvous 

 epidermis, marked on the anterior slope with transverse ziczac pur- 

 plish-brown streaks ; the umbonal ridge elevated and whitish, often 

 edged anteriorly with purplish brown; hinge-margin elongated, not 

 elevated, no dorsal angle ; anterior edge short, much arcuated, the 

 extremity dilated and rounded ; ventral margin incurvated, posterior 

 end prominent, rounded, much attenuated, with a few radiating cos- 

 tellae ; within, tinged with purple anteriorly. J. . 1 \. — Philippines. 



M. Patagonica D'Orbigng MSS. Oblong-subcuneiform, the 

 beaks being all but terminal and the posterior end narrowed and 

 obtuse ; the anterior broad, obtuse and flat ; hinge margin straight, 

 somewhat elevated and elongated, the anterior edge in the adult in- 

 stead of forming an angle, running at first almost in the same line 

 with it, and then suddenly sloping in a semicircle to the nearly 

 straight ventral margin ; cuticle greenish olive ; interior tinged with 

 purple, 1 . . 2 — Patagonia. 1 



Section B. 

 Smooth, oblong-subtrapeziform, the shape being intermediate between 



M. Modiolus and M. Lithodomus. 



M. Vagina Lam. 7. — E. vol. 2. p. 569. — Subrhombic-oblong, 

 subcylindraceous, white under a uniform yellowish chesnut, cuticle 

 very thin, pellucid, nearly smooth, marked only with close concen- 

 tric wrinkles ; dorsal edge a little arcuated, elongated, and sub- 

 parallel to the ventral ; anterior extremity much rounded : posterior 



1 To this section belong likewise the M. Castanea of Sag in the 

 second and. M. Capax of Conrad in the seventh volume of the 

 Journal A.N.S. of Philadelphia, Also the Prideauxii of Leach's 

 Zoological Miscellany. 



