APPENDIX. 335 



ad aream dorsalem posticam rufo tincta, lineis radiantibus crebris vix insculpta ; umbonibus 

 eminentibus ; extremitatibus rotundatis, rufo biradiatis ; intus citrina sanguineo conspersa ; 

 margine argute crenulato. Plate XI, figures 21, 22. 



Shell small, thin, inequilateral, rounded ovate, moderately ventricose, surface smooth and 

 shining, with very delicate lines of growth, and numerous, indistinct, radiating stria?, more 

 distinct posteriorly and near the margin ; anterior end broadly rounded ; posterior end narrowed, 

 semi-rhomboidal, the dorsal margin rather rapidly declining ; color pale lemon, or straw-color, 

 somewhat discolored or blotched with rufous, the beaks biradiate with brown, and the posterior 

 dorsal area brownish ; interior bright lemon-color, beautifully stained with dark liver-brown, 

 especially near the beaks and posteriorly ; inner margin minutely crenulated. Height and 

 length five-eighths of an inch ; breadth three-eighths of an inch. 



Locality. Inhabits San Pedro. Wm. P. Blake. 



Compared with C. Elenense, Sowb. , it is much less elevated and differently colored, though 

 the general characters are very closely allied. It is more like C. Mortoni, Con-., but is less solid, 

 inequilateral, less truncate posteriorly and more freely colored within, and the internal margin 

 in that shell is not crenulated. 



TAPES GRACILIS, Gould. 

 [Preliminary Report, &c., 1855.] 



Testa parva, tenuis, inequilateralis, elongato-ovata, albida, obsolete fusco radiata, ad aream 

 dorsalem posticam fuscata, concentrice striolata ; extremitatibus rotundatis, extr. antico acutiore ; 

 intus Candida. PI. XI, figures 19, 20. 



Shell small, thin, transversely elongate-ovate, rather compressed, beaks, at the anterior third, 

 whitish, with traces of dusky radiations on the disks, and clouded with dusky on the dorsal 

 areas; surface with very fine concentric lines of growth, coarser at the ends; extremities 

 rounded, the posterior somewhat obliquely, the anterior narrower and somewhat more acute ; 

 anterior dorsal area depressed, without any line of demarcation ; interior white. 



Length three-fourths of an inch ; height half an inch; breadth an eighth. 



Locality. Brought from San Pedro by Mr. Blake. 



Belongs to the group with T. florida and geographica, but is less inequilateral and less angu- 

 lar than those shells, It may grow much larger than the present specimen, and is pretty 

 certain to vary in coloring. 



In addition to the preceding are two or three species left undetermined in consequence of im- 

 perfect specimens, or because the characters are not sufficiently marked to render their novelty 

 decisive. The following remarks may be added in regard to some of these : 



(1.) MYTILUS EDULIS, or very closely allied. It seems to differ in having the dorsal angle at a 

 greater distance from the beak the posterior dorsal slope more rapidly declining and more 

 curved, as in M. hamatus the interior more pearly, and the margin more uniformly deep black. 



Locality. San Francisco. 



(2.) OSTREA. A small parasitic Oyster, on twigs, probably of Gorgonia, usually projecting 

 equally to either side. The form is elliptical, the under valve having a groove for the twig, 

 with a corresponding eminence in the upper valve ; sometimes it adheres by but one edge, and 

 then assumes an oblique, alate form, like Avicula. It is quite thin, lineated, radiately orna- 

 mented with fasicles of brown lines. 



Locality. San Diego. 



