578 PROCEEDINOS OF THE NATIONAL MUSEUM. vol. 51. 



Arcularia exilis Powys, 1835. This is Nassa fontainei Orbigny, 1841, and pana- 



mensis Philippi, 1851, not of C. B. Adams, 1852. It ranges from Panama to Peru 



and Chile. 

 Ilyanassa obsoleta Say, 1822. This species has been introduced with "seed" 



oysters from the Atlantic coast, and at last accounts was flourishing on the oyster 



beds in San Francisco Bay. 



The only recorded recent species from this region of which I have 

 not seen specimens and which are not contained in the collection of 

 the United States National Museum are Arcularia paposana Philippi, 

 1860, from Paposo, Chile; f estiva Powys, 1835, Panama to Guaya- 

 quil; and sparta Marrat, 1897, from the " west coast of South America." 



The following forms near to or usually associated with the Nassas, 

 may not improperly be included here: 



Genus PHOS Montfort, 1810. 



Phos cocosensis Dall, 1896. Gulf of Panama, Cocos Island. (Gulf of California?) 



Phos crassus Hinds, 1844. Lower California and the Gulf of California. 



Phos chelonia Dall, new species. Shell very similar in general appearance and 

 size to P. varicosus Gould, having similar whitish varices, about three or four 

 to a whorl, but differing by ha\T.ng the whorls appressed to the suture, not deeply 

 impressed, and in having a nuclear shell of five or six whorls, deeply spirally sul- 

 cate instead of a nearly smooth one of three and a half whorls. The color of the 

 present species is pale yellowish with a tinge of brown, as in vaiicostis, which also 

 has narrower and more numerous ribs between the varices. (Cat. No. 194961, 

 U.S.N.M.) Dredged at the Galapagos Islands in 40 fathoms. 



Phos altematus Dall, new species. Shell resembling P. cancellatus in a general 

 way, but without the nodose-prickly sculpture. WTiorls six with two or three 

 nuclear turns in atldition. Suture distinct, not deep, spire about as long as 

 the aperture; sculpture of narrow, nearly straight, axial ribs with wider interspaces, 

 about 22 on the last whorl, extending to the base; these are overridden by (be- 

 tween the sutures five) flattened, straplike spirals, with narrower channeled 

 interspaces, in which are two or three very fine distinct spiral threads. The 

 intersections are not nodulous, though the spirals are undulated where they 

 cross the ribs. The outer lip is hardly thickened, not varicose but lirate within, 

 the pillar simple with a sharp basal fold. Length, 26; width, 12 mm. (Cat. No. 

 212110, U.S.N.M.) This species like most of the others is occasionally banded 

 with brown. The specimens examined are from the Gulf of California. 



Phos mexicanus Dall, new species. Shell small, slender, not unlike P. articu- 

 latus Hinds, but without the articulations; with only 10 ribs on the last whorl 

 instead of 14; with eight or nine whorls; the suture appressed, the spiral sculpture 

 of flattish threads, larger and flatter on the base; between sutures two or three 

 spirals more prominent than the rest and swollen where they pass over the axial 

 ribs; aperture simple, lips not callous, pillar without a keel anteriorly; the canal 

 short, the siphonal notch deep. Length, 23; diameter, 8.5; length of last whorl, 

 13 mm. (Cat. No. 212111, U.S.N.M.) Ranges from Cape St. Lucas to Panama. 



Phos minusculus Dall, new species. Shell very small and thin, with about six 

 whorls -^vithout the nucleus; whorls rounded, suture distinct, with two undu- 

 lated spiral threads in front of it, and in front of them six flattened threads with 

 wider channelled interspaces between the sutures on the penultimate whorl; 

 these are not swollen when they cross the ribs, of which on the last whorl there 

 are 14, with wider interspaces; there are no intercalary spirals; outer lip slightly 



