WOODWARD HIPPURITID^. 55 



into an operculum, the second remaining filiform ; 4thly, the shell- 

 structure is different *. 



IV. M. Charles Desmoulins {Bull. Soc. Linn. Bordeaux, 1827) 

 regarded the Hippurites and Radiolites as a peculiar order of Mol- 

 lusca, combining the attributes of the Tunicates and Sessile Cirri- 

 pedes. 



These -vdews appeared less unreasonable at a time when the Cirri- 

 pedes were supposed to be Molluscous animals. Nevertheless, this 

 was strongly contested by M. Deshayes, and by M. Sander Rang, who 

 gives an excellent summary of the arguments on both sides, in his 

 Manuel des Mollusques (1829). He terms the connection of the 

 Hippurites vdih the Cirripedes and Tunicates " an unnatural asso- 

 ciation," and says that the arguments for it are contrary to reason 

 and experience. The cellularity of the Hippurite is, like that of a 

 shell, independent of the animal, and not like the tubes of a Balanus, 

 which are occupied (as Cuvier showed) by processes of the mantle. 

 The shell of the Balanus is conical, and consists of several elements 

 which enlarge independently. Its operculum also consists of several 

 pieces ; and both are symmetrical -f. 



V. Dr. Carpenter, in his *' Report on the Structure of Shells" 

 {Trans. Brit. Assoc. 1845, p. 15), expressed his opinion that the 

 Hippurites were intermediate "between the Ostracece and sessile 

 Balani." Dr. Carpenter informs me that he was led to think they 

 could not, be bivalves, on account of their openly cellular walls ; but 

 the numerous instances of strata of empty cells in both recent and 

 fossil Oyster-shells proves that this character cannot be relied on X- 



Sir C. Lyell formerly entertained the conviction that the Radiolites 

 Mortoni of Mantell belonged to the genus Conia {Mag. Nat. Hist. 

 1836, vol. ix. p. 104). 



VI. Dr. Goldfuss, at the conclusion of his great work, Petref. 

 Germ. (1840), describes the Hippurites as Brachiopoda, placing 

 them next to Crania. Some of the difficulties in the way of this 

 view were, however, unknown at the time. 



The essential characters of the Hippurites, which separate it from 

 the Brachiopoda, are — 



1 . The shell is composed of three layers, which is not the case 



in any Brachiopod. 



2. The prismatic-cellular structure is like that of Pinna and 



JEtheria, and not like that of the Brachiopoda. 



3. No Brachiopod has a sub-nacreous shell with water-chambers. 



* The shell-structure of the Anellides has been usually described from prepara- 

 tions of Dentalium or Vermetus, both of which are Gasteropods. 



t Ferruca is unsymmetrical, only because a portion of the operculum is ce- 

 mented to the shell, indifferently right or left {Darwin). Tubicinella, the only 

 cylindrical Balanus, is so from its pecuHar habitat, in the skin of the Whale ; it is 

 conical when young, but, as the skin of the Whale wears away, the Tubicinella 

 also sheds the summits of its valves, and grows downwards deeper and deeper 

 (Gray). 



t Especially the recent Ostrea purpurea, Gray, and the fossil O. vesiculosa and 

 0. bellovacina. 



