NO. 2094. MOLLUSKS OF THE GENUS RIS80INA—BARTSCIL 51 



RISSOINA CONTABULATA Morch. 



Rissoina contabulata Morch, Mai. Blatt., vol. 7, 1861, p. 68. 



Shell cylitidric, scalate, with straight, distantly spaced, axial ribs. 

 Of these ribs, which are squarish, about 14 occur upon the last 

 turn. They are sharply cusped at the summit and joined together 

 at the periphery by a strong spiral cord. Suture channeled. The 

 axial ribs on the last whorl are joined on the middle by a squarish 

 spiral cord. Columella encircled by a spiral cord. Aperture trian- 

 gular lunate. Length, 3 mm.; diameter, 1 mm. A single specimen 

 from Sonsonate. 



To the above Morch adds: 



Rissoa scalaris Freni. Mon., fig. 32, has a great resemblance to this species, and has 

 likewise a decollated apex. Rissoa notahilis Adams, Pan. Shells, p. 181, is not unlike 

 it. The axial ribs and the two basal keels are angular with very deep interspaces. 



Carpenter, ^ makes the following statement regarding the Rissoa 

 notahilis: 



After drawing this unique shell carefully under the microscope, and making copious 

 notes on the diagnosis from the specimen, an untoward cough lodged it amono- the 

 meshes of the curator's carpet, whence I endeavored in vain to extricate it. This 

 unfortunate accident, however, is the less to be regretted, as I can state with perfect 

 confidence that it was exactly identical with another shell in the collection, p. 255, 

 q. v.; and with M. 498, Parthenia quinquecincta. The "concave summits" of the ribs 

 imply that the ribs are sharp, with concave interstices; and the "upper keel " is simply 

 due to the angulation of the whorls. Though the lip was broken, the columellar plait 

 as well as the sinistral apex, escaped the professor's notice. 



RISSOINA HISTIA, new species. 

 Plate 33, fig. 9. 



Shell minute, highly polished, milk white. Nuclear whorls a 

 little more than one, smooth, well rounded. Postnuclear whorls 

 moderately rounded, appressed at the summit, polished, marked by 

 exceedingly fine, microscopic, incremental lines only. Sutures moder- 

 ately impressed. Periphery of the last whorl well rounded, marked 

 by a single incised line. Base moderately long, well rounded, pro- 

 vided with a strong fasciole anteriorly, polished, marked by a single 

 incised line which is a little anterior to the peripheral one which it 

 equals in length. Aperture very irregular in outline, oblique, chan- 

 neled anteriorly and posteriorly; outer lip claw-shaped, twisted and 

 sinuous, having a little projection in the middle of the basal line 

 reinforced immediately behind by a strong varix; inner lip thin, 

 appressed to the base with which it becomes completely fused, 

 the continuations of the curved basal fasciole being responsible for 

 the projection on the basal lip. 



The type, Cat. No. 151927, U.S.N .M., and another specimen were 

 dredged by the U. S. Bureau of Fisheries steamer Albatross at stations 



1 Proc. Zool. Soc. London, lSfi.3, p. 189. 



