346 Mr. W. H. Benson on the genus Pterocyclos. 



notoma appeared. In 1843 Sowerby published his monograph 

 of Cyclostoma, including a new species, C. bilabiatum (for which 

 " Pterocyclos, Benson/' was given as a synonym), and refigured 

 Pearson's hispidus as C. spiraculum. In March 1844 Pearson's 

 hispidus suffered a further change of name, being published in 

 Philippi's work under Von dem Busch's name of Steganotoma 

 Princepsi, and Pt. rupestris was again figured as St. pictum, 

 Trosch. : Prinsep's name (with an erroneous spelling) being affixed 

 to the former species, it is possible (though the source is not 

 acknowledged) that the specimen was originally derived from 

 him, in which case it was unfortunate that the shell should not 

 have been accompanied by a note of the previous publication of 

 the genus and species. 



The following are the species known to me, with their syno- 

 nyms. Nos. 4 and 5 are I believe as yet undescribed. Coloured 

 figures of them by Dr. Bland were sent to me for inspection by 

 Prinsep. The original shells may yet be forthcoming in some 

 English collection. 



1 . Pterocyclos rupestris, Benson, J. A. S. vol. i. January 1832, pi. 2. 

 Steganotoma pictum, Troschel, Wieg. Archiv, 1837 ; Abbildung. 



Phil. 1844. 



2. Pt. hispidus* (Spiraculum), Pearson, J. A. S. vol. ii. 1832. 

 Cyclostoma spiraculum, Sow. Thes. Conch. 1843. 

 Steganotoma Princepsi, V. d. Busch, Abbild. 1844. 



3. Pt. parvus (Spiraculum), Pearson, lac. cit. pi. 20. 



4. Pt. (unnamed), note by Dr. Bland, J. A. S. vol. v. p. 783, 



Ceylon. 



5. Pt. (ditto), Dr. Bland, loc. cit. Pulo Susson near Pulo Pi- 



nang. 



6. Pt. bilabiatus (Cyclostoma), Sowerby, Thes. Conch. 1843. 



Dr. Philippi alludes to a species in the possession of Dr. Pfeiffer 

 which is undescribed, unless it be P. parvus or bilabiatus, to which 

 last Dr. Philippi has not adverted in the ' Abbildungen.' His 

 arguments for the separation of the genus from Cyclostoma, in 

 opposition to the opinion of Deshayes, grounded on the analogy 

 to Pleurotoma afforded by the slit in the lip, and on the thimble- 

 shaped operculum, are worthy of attention. The planorbular 



* Since the above went to press I find that Dr. Pfeiffer has, in the 

 ' Zeitschrift ' for 1846, p. 35, under the head of Cijcl. bilabiatum, Sow., 

 acknowledged the priority of Pterocyclos, Benson, to Troschel's Stegano- 

 toma ; and has referred bilabiatum, and spiraculum, Sowerby, to Pterocyclos. 

 He gives C. angnlifera, Souleyet, ' Rev. Zool.' 1841, as synonymous with 

 C. spiraculum, and proposes to cancel Sowerby's name in favour of the 

 latter ; both, however, must give place to Dr. Pearson's specific name of 

 " hispidus." 



