P T E II C Y C J. S . 



Plate I. 



Genus PTEP.OCYCLOS, Bciuson. 



Testa peramplikr umhiUcuta , phis miiiiis dlscoitlea, fiihes- 

 cenle, castaneo vel nstulalo-brmineo varie fasc'uda et 

 nndidafo-maculala, spird ckpressd, anfractibits angus- 

 tis, rotimJatis, ultimo hderdum soliito, tubido parvo 

 in suturam pone aperturam seepe munito ; aperturd 

 circulari, labro diipticato, peritmnate externa nunc in 

 alam sinnosam nunc in tubidnm productu. 



Operculum calcareum, ictrinque Immnatum, inter laminns 

 erecte spiraliter lamellatum, laferlbus interdiim sub- 

 (squiditer concaviusculis, interdiim latere externo pla- 

 niusculo, interna valde concavo. 

 Shell very largely urabilicated, more or less discoid, ful- 

 vous, variously banded and wave-spotted with chest- 

 nut or burnt-brown, spire depressed, whorls nai-row, 

 rounded, the last sometimes uncoiled, often furnished 

 with a small tube in the suture behind the aperture ; 

 aperture circular, lip duplicate, outer peritrenie pro- 

 duced, sometimes into a sinuous wing;, sometimes 

 into a tube. 

 Operculum calcareous, laminated on each side, and erectly 

 spirally lamellated between the laminae, sides some- 

 times equally slightly coneave, sometimes rather flat 

 on the outer side, very concave on the inner. 



The shells associated in this genus are distinguished 

 by the curious feature of a winged sinus being developed 

 at the upper margin of the lip on arriving at maturity 

 (Vterocydos proper). In some the marginal sinus is 

 modified into a spouted tube (Rhiodoma); in others, a 

 spouted tube is developed at the marginal sinus before 

 the shell is mature {Opistl/oporus), and remains at a 

 greater or less distance behind the aperture. All three 

 forms of Pterocyclos have been introduced and minutely 

 described under the foregoing generic names by Mr. Ben- 

 son. They are natives chiefly of Bengal, Buriuah, Siam, 

 Ceylon, and the islands of the Eastern Archipelago. 

 What especial filaments of the animal correspond with tiiis 

 sinus or tube, no one has yet been able to show. Mr. 

 Arthur Adams has described the external characters of the 

 animal from a specimen collected as far north as Tsu- 

 Sima, in the Korea Strait, but no mention is made of the 

 relation between the soft parts and the particular structure 

 which characterizes the genus. 



Along with the modification of the sinus, there is also a 

 modification of the oprrodum. It is composed in both 



groups of two laniiuffi, between which is an erect s])iral 

 lamella. In Pteroci/clos proper the spire is pushed out 

 as it were from tlie inner side, which is thus rendered ex- 

 ceedingly convex ; in theOpist/ioporus and i?//ws/oi«ffgrou)is 

 the inner and outer laminae are almost equally slightly 

 concave, and as each lamina reaches at its circumference 

 beyond the intervening erect lamellse, the operculum has 

 the appearance of a pulley (Recluz) or vertebra of a fish 

 (Benson). 



Species 1. (Fig. a, b, Mus. Cuming.) 



Pterocyclos bifrons. Pier, testa perampUter aperte 

 umhilicatd, discoided, supra peripheriam purpureo-cas- 

 taned etfulvd, infra violaced, immaculatn, aufractlbus 

 rolundatis, superne arcuato-strialis ; aperturd oblique 

 circulari, sinu latiuscnlo, fumido. 



The two-faced Ptekocyclos. Shell very largely 

 openly umbilicated, discoid, above the periphery 

 inirple-chestuut and fuhous, below violet, unspotted, 

 whorls rounded, arcuately striated at the upper part ; 

 aperture obliquely circular, sinus rather broad, swollen. 



Pfeiffek, Pro. Zool. Soc. 1855, p. 117. 



Hab. Cejlon. 



Named bifrons from the circumstance of the chestnut 

 colouring terminating abruptly at a lino encircling the 

 shell at its periphery. 



Species 2. (Pig. a, b. Mus. Cuming.) 



Pterocyclos pabilis. Pter. testa modic'e perspective um- 

 bUicatd, suh(/loljoso-turbinatd, soUdiusculd, albidd, 

 fuho -castaneo infra peripheriam fasciatd, supra un- 

 dulato-flammatd, anfractibus declivi-rolmidatis, ad su- 

 turas mar/jinatis; aperturd subampld, labro crassi 

 refiexo, sinu brevissimo, subobsoleto. 



The like Pterocyclos. Shell moderately perspectively 

 umbilicated, rather solid, somewhat globosely tur- 

 binated, whitish, banded below the periphery with 

 fulvous-chestnut, nndulately flamed above it, whorls 

 slopingly rounded, margined at the sutures, apertui-e 

 rather large, lip thickly reflected, sinus very short, 

 almost obsolete. 



Pfeiffer, MS. in Mus. Cuming. 



Hab. ? 



February, 18(13. 



