208 Kansas Academy of Science. 



Superfamily Veneracea; Family XXVII VENERlDiE. 

 Subfamily Venerin-^; Genus Tivela Link. 



"Shell triangular, subequilateral, cuneiform; three to five car- 

 dinal teeth in one valve, four to six in the other; anterior lateral 

 tooth narrow, elongated, compressed; pallial impression with a 

 short oblique or sometimes horizontal sinus."''' 



37. Tivela craisatelloides Conrad. Plate IV, fig. 37; times, one-half. 



Cytherea (Trigonella) crassatelloides Con., Jour. Phil. Acad. Sci., vol. VII, 

 1837, p. 253, pi. XIX, fig. 17. Hinds. Voyage Sulphur, p. 65, pi. XXI, 

 fig. 1, 1844; equals Z)owaa; stultorum Marve, Linne, Lyst. Conch., pp. 37, 

 40, pi. IX, fig. 7, 1823; equals D. stultorum Mar., Gray, Index, Test. 

 Suppl., pi. II (Donax), fig. 2, 1828. 



Cytherea crassatelloides Con., Hanley, Descr. Cat. Rec. Bivalve Shells, p. 

 ■ 106, 1843. Sowerby, Thes. Conch., vol. II, p. 612, pi. CXXVII, figs. 1-3. 

 Reeve, Conch. Icon., vol. XIV, pi. I, fig. 3, 1864; equals Cytherea stul- 

 torum Gray, Hanley, Descr. Cat. Rec. Bivalve Shells, p. 1Q6, 1843; equals 

 Trigonella crassatelloides Con., Jour. Phil. Acad. Sci., vol. I, 1849, p. 

 213; equals Trigonia stultorum Gray, Deshayes, Cat. Conch. Coll. B. 

 M., part I, p 46, 1853; also Trigonia crassatelloides Con., Deshayes 

 (loc. cit.); ec[\iidAs Cytherea solodissima¥h\\. Gabb, Pal. Cal.,vol. II, p. 96. 



Pachydesma crassatelloides Con., Proc. Phil. Acad. Sci., 1854, p. 121. Car- 

 penter, Brit. Assn. Rept., 1863, p. 640. Cooper, 7th Ann. Rept. Cal. St. 

 Min., 1888, p. 256. Keep, West Coast Shells, p. 189, fig. 62. Tivela 

 crassatelloides Con., Williamson, Proc. U. S. Nat. Mus., vol. XV, 1892, 

 p. 187; equals Cytherea {Tivela) crassatelloides Con., Stearns, Proc. U. 

 S. Nat. Mus., vol. XXI, 1898, pp. 371-378, pis. XXIII-XXV; also Nauti- 

 lus, vol. XIII, 1899, p. 73. Arnold, Mem. Cal. Acad. Sci., vol. Ill, p. 

 143, 1903. 



Shell large, thick, almost equilateral-triangular in shape, ventri- 

 oose; umbones subcentral to slightly anterior to center, not very 

 prominent; anterior dorsal margin straight to near middle trans- 

 verse line of shell, rather equally rounded at base; posterior mar- 

 gin sharp, nearly straight; posterior extremity more obtusely 

 rounded than anterior (in some cases it is almost angular); ventral 

 margin elliptically to prominently and evenly arcuate; surface 

 sculptured with very fine to very coarse incremental lines accord- 

 ing to age of specimen; a posterior submarginal angular ridge is 

 shown on some specimens, but is nearly or entirely obsolete in old 

 specimens; cartilage-pit triangular, not wide, rather deep, sepa- 

 rated from posterior ligamental groove by a prominent thick ridge; 

 cardinal ridges (teeth) three in number, prominent, thick, anterior 

 lateral tooth elongated. 



Dimensions of medium-sized mature specimen: Lat., 96; alt , 80; 

 diam., 37; umbones to anterior extremity, 69^, to posterior ex- 

 tremity, 72. 



The specimens of this species obtained differ from the Mactras 

 in being more equilateral-triangular in shape, by being less gib- 



57. After Arnold (see below). 



