174 Account of Oxygyrus, a new Species [March, 



from its most obvious distinguishing character, the rapidity of con- 

 volution, I have named Oxygyrus. From o& s velox, and Tvpou incurvo. 

 Class — Gasteropoda, Cuvier. 

 Order — Nucleobranchi, Blainville. 

 Fam. Atlantida, Rang. 

 Genus, Oxygyrus, mihi. 



Char. Gen. Testa subcartilaginosa, discoidea, cito convoluta, duo- 

 bus lateribus similibus, utroque latere profunde umbilicata ; anfractibus 

 exterioribus antecedentes fere amplectentibus ; anfractu ultimo late et 

 acutissime carinato ; carind ab ore usque ad dimidium periferice extensd, 

 illuc desinente, extremitate angulatd ; nperturd cordiformi, sinu carinam 

 intrante. 



Operculum cordiforme, medio depressum, sabcanaliculatum. 



Animal spirale, capite proboscidiformi, tentaculis duobus brevibus 

 cylindraceis, oculo magno saliente ad basin exteriorem munitis ; ore 

 terminali ; branchiis pectiniformibus, inter jecur et penem oblique 

 sitis ; pede aid natando aptd, foliaced, lobis duobus pr&ditd ; lobo 

 majore versus extremitatem dilatato, cyatho ad latus posito ; minore 

 oblongo-ovato, membranaceo, tenuissimo, margine dentato, quasi rupto, 

 operculum facie inferiore gerente ; operculo corneo. 



Shell subcartilaginous, quickly convolute ; the first whorls being 

 nearly enveloped hy those succeeding, discoid, symmetrical, deeply 

 umbilicated on each side ; last whorl broadly and sharply keeled from 

 the edge of the mouth to about half the circumference ; keel angular 

 at its posterior termination ; aperture sinuous, heart-shaped, not entire, 

 being encroached upon by the preceding whorl ; peiitreme acute, with 

 a narrow slit or sinus on the front edge, running into the keel, which 

 is there double. 



Operculum heart-shaped, depressed, and channeled with a medial 

 line. 



Animal spiral. Head proboscidiform, with two short cylindrical 

 tentacula, having a large prominent eye on the exterior base of each. 

 Mouth terminal. Branchiae pectiniform, lying obliquely between the 

 liver and the male organ. Foot a foliaceous swimmer, having two 

 lobes, the larger widening toward the extremity, and having a lateral 

 sucker ; the smaller lengthened anteriorly, extremely thin, jagged, 

 and bearing the operculum on its under surface. Operculum horny. 



The animal much resembles that of Atlanta, but differs in the form 

 of the greater lobe, the position of the sucker, and the foliaceous 

 appendage to the operculated lobe of the foot, which is traversed by 

 veins having the appearance of tendons, which admit of the contrac- 

 tion of the organ. The proboscidiform head is more swelled towards 



