NO. 1312. 



SYNOPSIS OF THE VENERID^—DALL. 385 



The more northern specimens arc smaller and more oval than those 

 from Santa Barbara, the type locality; and the purph- streaiv is 

 reduced to a more or less distinct flush, which is occasionally wholly 

 absent. These characters, however, seem hardly pronounced enough 

 to deserve a varietal name. 



TIVELA PLANULATA Sowerby, 1829. 



Gulf of California. (Julf of Tehuantepec, and southward to the 

 coast of Ecuador. 



This includes the variety sujfasa Sowerby, 18;-^5; Donax lesson) 

 Deshayes, 1835; Oytherea undulata Sowerby, 1851, a color variety; 

 and a mactroides Lamarck, 1818, not of Born, 1778. It is extremely 

 variable in coloration, but maintains fairly well its compressed trian- 

 gular form. 



TIVELA HIANS Philippi, 1851. 



Magdalena Bay, Lower California, to Valparaiso, Chile. 



This form, described from Mazatlan, is more elongated and i-ostrate, 

 has a more livid purplish coloration and a very distinct gape behind, 

 by which it is separated from T. pJanulata. 



TIVELA ARGENTINA Sowerby, 1835. 



AVest Mexico and south to Panama. 



Distino-uished bv its yellowish- white color, thin shell, and arcuate 

 form attenuated at both ends. It is GytKerea ^quilatem Deshayes, 



TIVELA ARGUTA Romer, 1864. 



Gulf of California to Panama. 



Shell small, thin, and oval, recalling T. trigonelh, of the Antilles. 



TIVELA GRACILIOR Sowerby, 1851. 



Puntarenas, Costa Rica. j. , r 



This is a species of peculiar form, with tine elevated radial lines 

 anteriorly. It is not the shell figured by Komer under this name. 



TIVELA BYRONENSIS Gray, 1838. 



Scammoivs Lagoon, Lower California and the Gulf of California, 

 and southward to the coast of Ecuador. 



This is r. y.«.Z.V/to Sowerby, 1835, notof Megerle, IsU: \enmeolan- 

 r/.m'.'.0rbignv,181T; Oytherea stultorum Menke, ^'^■^'- '^^^^ ";/™^; 

 1823; Cythereaco,^lc^daM^r^, 1817, notot Lamarck, ^^^"^iJ^'J^'^'''^ 

 pidla Philippi, 1851, and perhaps 0. irdermedia Sowerby, 1851, and 1. 

 elegansY^vr\\\,mO. ^,v>,^« At.m7'/. Carpenter, 185 <. appears to be 

 the young frv of this species: T. semifdva Menke ^^ ^ ^^fy ^^'^^^^ 

 variety, and 'j: /i/../.// Hanley, 1811, is a striped and la^icecl cohn 

 form of the young shell. It is the most comm<ni ot he 1 acih< (oast 

 species and the analogue of T. madroldcs of the Antilles. 



