220 UNITED STATES GEOLOGICAL SURVEY OF TOE TERRITORIES. 



Genus GONIOMYA, Agassiz. 



Synon.—Mya (sp.), Soworby (1814), Miu. Conch., Ill (not of Linnaeus). 



Goniomya, Agassi/. (lSIM), Verhandl. d. Schweiz., 102 ; and (1842) Etnd. Crit. Sur. les Moll. Fobs., 



I ; also, Germ. Trausl. Sow. Min. Conch. (1842), 275. — Meek and Haydeu (1856), 



Proceed. Acad. Nat. Sci. Philad., 81 ; and others. 

 Lysianassa, Munster (1838), Goldf. Petref., II, 2G2 (not M. Edwards). 

 Pholadomya (part), d'Orbigny (1844), Pale"ont. Fr., Terr. Crdt., 111,348; Prodr. de Pal. (1850), 



II, 49.— Pictet (1855), Traite". de Pal., Ill, 370.— Gabb (1861), Synopsis Mollusca of the 



Cretaceous Formation, 164 (not Sowerby). 



Eiym.—yuvla, au angle ; Mya. 

 Type. — Mya angulifera, Sowerby. 



Shell transversely elongate-oval, or oblong, rather convex, or more or 

 less compressed, nearly or quite equivalve, generally inequilateral ; inner 

 layer pearly, outer subcorneous; extremities rounded or subtruncated, 

 and gaping, the posterior hiatus being larger than the anterior; beaks 

 depressed, contiguous, or approximate, submesial, or more or less in advance 

 of the middle; ligament short, external or marginal ; cardinal margin slightly 

 thickened under the beaks, but without teeth ; surface minutely granular, 

 concentrically striated, and ornamented with costas that are neither radiating 

 nor parallel to the marks of growth, but descend and converge from the 

 dorsal side before and behind the beaks, so as to connect along the flanks in 

 a series of nearly equal angles, or by little short horizontal extensions ; mus- 

 cular scars faintly marked ; pallial line unknown. 



Although Goniomya is_ allied to Pholadomya, and by several authors 

 included in that genus, these two groups can readily be distinguished by the 

 peculiar divaricately-arranged costse of Goniomya ; those of Pholadomya 

 always radiating from the beaks. Goniomya also has its surface occupied by 

 numerous minute granules, not yet, I believe, seen on Pholadomya. There 

 were, doubtless, likewise corresponding differences in the animals of these 

 genera. 



The granules of Goniomya are arranged in radiating rows, and seem (<> 

 be confined to the outer subcorneous layer of the shell. Precisely similar 

 minute granules are also seen on Myacites, Attorisma, Cheenomya, Sedgwickia, 

 and other allied genera, both recent ami extinct. It is also proper to 

 inform the student that even the peculiar divaricating character of the costa? 

 seen in (Jonio)>iya, is sometimes assumed by species of very widely distinct 



