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, loc. 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 Cycl. 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. angulifera, 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.” 
