300 University of California Publications in Geology [Vol. 9 



SPISULA CHICOENSIS, new name 



Plate 27, figures 6 and 7 



Lutraria truncata Gabb, Pal. Cal., vol. 1, p. 154, pi. 22, fig. 128, 1863. 

 Spisula truncata (Gabb), Dall, Trans. Wagner Inst. Sci., vol. 3, pt. 4, 

 p. 879, 1898. 



This species was described by Gabb as follows: 



Shell thin, compressed, somewhat elongated, length compares with the 

 breadth as about four to three; beaks nearly central, small, acute and 

 slightly inclined forwards; anterior cardinal margin slightly sinuous, pos- 

 terior convex, nearly straight; anterior end rounded; posterior obliquely 

 truncated, gaping. Surface marked by faint irregular lines of growth. 



Only part of the hinge of the left valve is known. Hinge plate 

 wide, resilifer very narrow, long, with raised margins, which appear 

 as a prominent toothlike ridge arising from the posterior margin 

 of the chondophore ; resilifer not roofed nor overhung by the 

 cardinal arm ; cardinal very prominent, high, arms of equal length, 

 extending nearly across the hinge plate ; ventral sinus excavated ; 

 anterior lateral partially destroyed; it is high and arises from the 

 ventral margin of the plate, extending nearly to the dorsal margin 

 of the shell, at some distance from the arm of the cardinal ; posterior 

 lateral short, nearly parallel to the ridge bounding the chondophore. 

 Pallial sinus unknown. The dimensions, as inferred from the figure 

 of the type are : length, 50 mm., height, 35 mm. A specimen from 

 the type locality measures: length, 49 mm., height, 36 mm., con- 

 vexity, 8 mm. 



Spisula chicoensis is quite constant in general shape, which 

 strongly suggests that of a Tellina. This form would not easily be 

 confused with any known coast Mactrinae. 



The specific name truncata was used by Montagu in 1808 for a 

 species that later became known as Hemimactra truncata: 25 It is 

 necessary to rename Gabb's species, because the genus Hemimactra 

 has since been reduced to the rank of a subgenus under Spisula. 



This species was described from specimens obtained from Pence's 

 ranch, (Pentz Post Office) Butte County, California. 



Occurrence. — Cretaceous: Chico, Pence's ranch, Chico Creek, and 

 Mineral Slide, Butte County, California (Gabb). 



25 Conrad, T. A., Am. Jour. Conch., vol. 3, appendix, p. 33, 1868. 



