GASTEROPODA. 115 



The animal of this genus has recently been examined by W. Clark, Esq., who 

 considers it a highly organized Mollusc, and closely allied to the Trochidae. Some 

 notes upon the subject by that gentleman were obligingly sent to me for perusal 

 by J. Gwyn Jeffreys, Esq., of Swansea, with permission to give the following 

 extract from those remarks : " The Rev. M. J. Berkeley (in the Zoological 

 Journal, vol. v, p. 426, at the end of the first paragraph) says, ' It is highly 

 probable that the other minute British Dentalia will prove to possess an animal of 

 like structure,' that is, of his new genus Ditrupa, which is not a Mollusc, but a 

 genuine Annelidon. He is in error, as we have observed the animals of three 

 species of minute Dentalia, viz. D. w perforatum, trachea, glabrum, and we have 

 figured and described the first in our MS. They are all genuine Mulluscs, much 

 more highly organized than the Dentalia." He then gives copious anatomical 

 details of the animal, which in a work devoted only to the calcareous remains of 

 the Mullusca it is not necessary to repeat ; and concludes by remarking, that he 

 considers the animal of this genus to be a compound of Cerithium, Rissoa, Trochus, 

 and of his new genus Pherusa, possessing a thick, corneous, circular, and multispira] 

 operculum. Mr. Jeffreys further says there is little doubt of the accuracy of the 

 foregoing remarks, and that he has himself verified those observations. 



Dr. Fleming, in an article upon Conchology, published in the Edinburgh ' Ency- 

 clopaedia, 1817,' proposed the name of Caecum as a generic term for these little 

 tubular and imperforate Testacea, which, in his work upon the ' Philosophy of 

 Zoology,' he named Caecalium ; these shells were, however, afterwards transferred, 

 in his ' History of British Animals, 1828,' into the genus Orthocera. Captain 

 Brown, in his 'Illustrations of British Conchology, 1827,' gives figures of what 

 he considered as seven different species, under the generic name of Brochus, and 

 M. Philippi has described one species with the name of Odontidium ; while, in the 

 notes by Mr. Clark, these animals are described under the name of Dentaliopsis. 

 As priority undoubtedly belongs to Dr. Fleming's name of Caecum, I do not think 

 it can be fairly superseded by even the excellent and important anatomical details 

 of Mr. Clark. 



A species from the Eocene formation at Hordwell, found by Mr. Edwards, is, 

 as far as I know, the earliest appearance of this genus. 



1. Cecum trachea. Mont. Tab. XX, fig. 5. 



Dentalium trachea. Mont. Test. Brit. p. 497, t. 14, fig. 10, 1803. 



Cecum trachea. Flem. Edin. Ency. vol. vii, p. 67, 1817. 



Orthocera trachea. Flem. Brit. An. p. 237, 1828. 



Brochus trachiformis. Brown. Conch. Illust. pi. 1, fig. 10, 1827. 



Odontina (ex Phil.) Zborzewshy. 1834. 



Cecum trachea. S. Wood. Catalogue 1842. 



Dentalium trachea. Thorpe. Brit. Mar. Conch, p. 5, fig. 61, 1844. 



Dentaliopsis trachea. Clark. MS. 1847. 



