LETTER VIII. 



NEARLY STRAIGHT OR IRREGULARLY TWISTED SHELLS, WITH SIM- 

 PLE OR DIVIDED CAVITIES PENICILLUS DENTALIUM 



VERMICULARIA SERPULA......SILIQUARIA. 



* 



HAVING now arrived at those shells which are formed into nearly 

 straight, or partly spiral and partly straight, or irregularly contorted 

 tubes, some of which are inhabited by vermes and not by mollusca, I 

 have concluded it to be better to introduce these shells together here, than 

 to separate them according to the difference of their inhabitants. This 

 seems to be particularly proper, since several of these shells, as will be 

 seen, are known only as fossils, and consequently we can form no deter- 

 mined judgment respecting the animals which formed and inhabited 

 them. Besides, as several of these shells are concamerated, their exami- 

 nation will very naturally precede that of the shells of the next division. 



LXVII. Penicillus. A tubular shell, narrow, and rather spirally 

 turned at its origin, dilating into a club-form at the other end, which 

 terminates in a convex disk, beset with small tubular perforations. 



This shell, which is Serpula penis, Linn, has not been seen fossil ; 

 nor is the nature of its inhabitant known. 



LXVIII. Dentalium. A tubular, conical, slightly bowed univalve, 

 open at both ends. 



Mr. Brander found, among the Hampton fossils, two species ; the one 

 of which he considered as D. dephantinum, and the other D. entails. A 

 specimen before me, of the latter fossil, seems in no respect to differ 



