175 



Dr. Gould continued his descriptions of the species Helix, 

 from the Shells of the United States Exploring Expedition. 



Helix obolus. T. parva, discoidea, deorsum comprcssa, su- 

 pra planulala, infra concava, radiatim minulissimo et inequaliter 

 siriata, fusco-ferruginea, piceo tessellala : spira anfr. 5^ supra 

 excavalis, ultimo supcrne costato-carinato : apertura sub-rhom- 

 boidea ; fauce lamella unica secundum anfractum pcnuUimum 

 volvente. Lat. -i, alt. -r^^ poll. Hah. Taheiti. 



A most singular discoidal shell, resembling Planorhis vortex. 



Helix bursatella. Testa parva, per-variabilis, rotundata, 

 conica vel planulata, supra maculis fuscis et albidis alternanti- 

 bus flexuosis, tessellata, infra, cinereo-albida vel flammulis fuscis 

 flexuosis radiata, costis numcrosissimis acutis radianlibus lyrata : 

 subtus convexiuscula, interdum simplex, interdum concentrice 

 striata, nunc radiatim costellata, nunc albida, nunc fusco flammu- 

 lata : spira anfr. ad 8 externe excavatis, ultimo carinato ; sutura 

 impressa, plerumque marginata : apertura parva, transversa ; 

 fauce cum lamellis 7 volventibus, quorum 2 superiores, 1 colum- 

 ellaris, 4 remotis (1 supra, 3 infra carinam) ad labium ; labro 

 simplici ; umbilico cavernoso, in junioribus acctabuliformi, in 

 majoribus ad januam parvo, constricto, margine acuto, una cum 

 labio continue. Hah. Taheiti and Eimeo. 



The above characters are found combined in every possible 

 manner. The variations in size, color, solidity, and umbilicus, 

 may all be reasonably ascribed to differences in age, food, and per- 

 haps to the elevation, between 2000 and 5000 feet, at whicli they 

 were collected. The armature of the mouth and the peculiar 

 umbilicus, at first broad, and at maturity contracted, or pursed 

 up, so that the flattened edges of the whorls form a large spheri- 

 cal cavity, are the characteristic marks. Two principal varieties 

 may be noticed. 



«. Large, elevated, conical specimens, which are without mot- 

 tling, rib-like stricC, or revolving lines beneath. Lat. ^^q-, alt. fj^ 

 poll. 



§. Smaller, depressed specimens, more or less coarsely ribbed, 

 striated and mottled, both above and beneath. Lat. -^, alt. ^^ 

 poll. 



Helix tumulus. Testa parva, solida, flavida, orbiculato-pyra- 

 midata, basi sub-planu!ata, umbilico modico perforata : spira 



