WITH DESCRIPTIONS OF NEW GENERA AND SPECIES. 213 



I am indebted to Dr. Thomas B. Wilson for the opportunity of examining the 

 three foregoing species in different periods of growth, which removed all doubts 

 about the specific differences of each. The young nohilis has the same dilated form 

 as the old shell. The young of the other two species are on the contrary very 

 slender. In the variegatus and nohilis there is a much larger proportion of the dark 

 waved bands to the white or light coloured shell, and in every stage of growth the 

 former is thicker and heavier than in corresponding ages of the others. 



NAUTILUS. 



N. PERFORATUS. — Suborbicular, umbilicated ; margin deeply sinuous ; colour white with brown irregular 

 transverse rays, becoming distant, and inclining to flesh colour on the margin of the wider portion of 

 the shell ; margin of aperture blackish-brown within. Length 6i. 



This shell has been referred to N. umbilicatus, Chemnitz, {N. scrobiculatus of 

 Solander and Dillwyn,) but it has not the flattened sides nor wide umbilicus of that 

 species, and the rays are much darker. It more resembles the pompilius, but the 

 umbilicus and narrower aperture readily distinguish it. It is about the size of that 

 species. 



PETRICOLA. 



P. CALTFORNicA. — Saxicava californica. Journ. Acad. Nat. Sc. Vol. 7, pi. 20, fig. 9, 1837. 



Petricola arcuatn, Desh. Rev. Zool. par la Soc. Cuv. 1839, p. 358, Mag. de Zool. 1840, PI. 19. 



P. CARDiToiDEs, Cou. Suxicuva carditoides, Con. Journ. Acad. Nat. Sc, Vol. 7, pi. 20, fig. 8. 1837. 

 Petricola cylindrncea? Desh. Mag. de Zool. 184.0, PI. 20. 



SILIQUA, Megerle. LEGUMINARIA, Schim. 



S. NUTTALLir, Con. 



SOLECURTUS NUTTALLII, CoJl. 



S. MAxiMus, Gould, not Wood. 



SoLEN spLENDENs, C/ienu. lUus. Conch. PI. 8, fig. 3. 

 S. LuciDA, Con. 



SoLECURTUS LUCIDUS, COU. 



S. K,ADiATUs, Gould not Lin. 



TRIGONELLA, Co7i. 



An equivalved subtriangular bivalve, thick, smooth; cardinal teeth three in each valve; a rather distant 

 straight anterior lateral tooth in one valve, fitting into a double tooth on the opposite valve ; ligament 

 pit deeply excavated ; pallial impression with a considerable sinus. 



T. CRASSATELLoiDEs, Tioh. Joum. Acad. Nat. Sc. Vol. 7, p. 253, PI. 19, fig. 17. 



