f 



818 PROCEEDINGS OF THE NATIONAL MUSEUM. voL.xxm. 



the same time show no essential differences except of size. Another 

 specimen from 135 fathoms in Paget Sound measures 74 mm. in 

 extreme kMigth and about 28 mm, in diameter. I have seen some fos- 

 sil specimens which attained even larger dimensions. The shell recalls 

 M(/(j((.rlnus rostra f UK (Pecchioli) in almost every respect, but the distal 

 ends of the nvmphs do not project as strongly as in that species. 



THYASIRA CONIA Dall and Simpson. 



(Plate XLII, %. 2.) 



As this came to hand too late to l)e figured in the Porto Rico report, 

 I give a figure of the species here from the largest specimen obtained 

 in the vicinity of San Juan Harbor, in 310 fathoms, by the U. S. Fish 

 Commission. 



THYASIRA EXCAVATA, new species. 

 (riateXXXlX, %h. 12, 15.) 



Shell subovate, thin, white, with a pale yellowish periostracum; 

 sculpture of concentric incremental lines, and in each valve three 

 sharp and two or thi'ee obscure radial ridges. Beaks small, su))acute, 

 not prominent, distinctly prosogyrate; lunule and escutcheon well 

 developed, elongate, rather narrow, and emphatically excavated, i 

 bounded by a well-marked carina, which in the case of the escutcheon 

 is high, thin, and sharp, separated from another less acute radial keel 

 by a wide, deep sulcus; on the disk near the middle are two other 

 radials, evident but obscure, and another a short distance behind the 

 lunular carina. The surface occasionally shows a faint dusting of 

 microscopic granulation, which is usuall}^ abraded. Valves moderately 

 convex, the interior polished, the hinge edentulous, the nymphs slen- 

 der and delicate, the ligament narrow and more or less visible exter- 

 nally, the margin of the valve indented by the external ridges. Lon. 

 20.0, lat. 17.5, diam. 15.0 mm. 



Dredged by the U. S. Fish Commission in the Gulf of California, 

 between San Marcos Island and Guaymas, in 1,005 fathoms; bottom 

 temperature, 37*-". 6 F. Also off' Tillamook, on the coast of Oregon, in 

 780 fathoms, mud; bottom temperature, 37''\3 F. 



This species is markedly characterized by the deeply excavated and 

 sharply bounded escutcheon and lunule, in which respect it is not 

 closely approached by any other. 



THYASIRA TOMEANA, new species. 



(Plate XXXIX, fig. 3.) 



Shell moderately convex, subovate, concentrically sculptured with 

 inci-cmental lines and covered by a pale straw-colored periostracum. 

 Lunule small, ovate, lanceolate, moderately impressed; escutcheon 



I 



