1836.] Note on Pterocyclos of tlw Straits. 783 



V. — Note on the Genus Pterocyclos of Mr. Benson and Spiraculum of 

 Mr. Pearson. By Dr. William Bland. 



On the 27th of May last, I was fortunate enough to fall in with 

 a shell of this genus, on the islet of Susson, one of the Boontin group, 

 opposite to the peak of Queda, and in sight of Pulo-Pinang. 

 Although the general description of my specimen answers to those 

 above-mentioned, yet in some particulars it differs from both. The 

 mouth is circular, its upper half marked inside by a double slightly 

 raised line, from whence the pterygoid process is sent off which 

 overhangs and forms the sinus, but the inside edge of this process 

 does not touch the penultimate whorl as in Mr. Benson's shell, and 

 it certainly differs from those of Mr. Pearson. In the specimen of 

 Pulo-Susson, the sinus is -^ 5 of an inch from the rings above-men- 

 tioned to the outside arch, and from this arch to the extremity of 

 the wing which overhangs and forms the sinus is T a - - th of an inch ; 

 the wing in breadth is T % th, mouth thickened, which thickening is 

 carried on to strengthen the wing on its upper part. Shell one 

 inch in diameter, with dark orange zig-zag lines across the whorls^ 

 and a band of a darker colour running longitudinally on the centre 

 of the last whorl. Animal recently dead, but in a state of decay, so 

 that nothing could be made out of it. 



As one drawing is worth many descriptions, I have cut a leaf out 

 of my book, having two figures of the natural size of the shell in 

 question, No. 1, for your inspection ; and, to assist in elucidating the 

 history of this genus of beautiful shells, I have added another figure, 

 No. 2, found at Trincomalee. 



This shell has a small pterygoid process bending down, and in 

 contact with the penultimate whorl, extending gth of an inch in 

 front of the circular mouth, but no vestige of tube or sinus obtains 

 in this specimen ; lip thickened and reflected ; the shell having all the 

 appearance of maturity ; diameter T 7 5 th of an inch ; operculum convex, 

 horny-formed, of circular layers. 



Note on Dr. Bland's Paper. 

 The Susson species appears, from the drawing forwarded with the 

 description, to belong to the typical group of Pterocyclos, which 

 ^includes P. parvus and rupestris, and to be intermediate between the 

 latter species and hispidus, to the last of which it exhibits an approach 

 in the irregular aperture and dilated and thickened wing ; but in the 

 absence of a specimen for comparison, no specific character can be 

 assigned with safety. 



