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 Trochidse. Some notes 

 upon the subject by that gentleman were obligingly sent to me for perusal by J. G\syn 

 JefiFreys, 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. imperforatum, trachea, 

 glabrum, and we have figured and described the first in our MS. They are all genuine 

 Molluscs, 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 Mollusca 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 

 multispiral 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 ' Encyclo- 

 paedia, 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 Fleming's name of Caecum, I do not think it can be fairly superseded by even the 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. C^CUM 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. 6", 1817. 



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



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



Odontina (ex Phil^ Zhorzeivshy. 1834. 



Cecum trachea. .S. Wood. Catalogue 1842. 



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



Dentaliopsis trachea. Clark. MS. 1847. 



C. Testa minutd, cylindricd, arcuatd, crassd, politd ; transversim rugulosd ; antice apertd, 



margine annulatd; postice oblique truncatd, submucronatd. 



