Mr. J. E. Gray on the Genus Rhizochilus. 479 



and very much resemble the Vermetus suhcanceJlahis, Phihppi, 

 Moll. Sicil. i. 172. t. 9. f. 20, who obsenes it is very frequent in 

 Sicilv; but Dr. Pbilippi does not describe the contraction of the 

 mouth of the tubes, and hence it may be a different species. He 

 refers to Chiaje's continuation of Poli, t. 57. f. 18, as ginng a 

 good figure of the animal of his species. 



Chiaje, who gives no description to the plates, figures three 

 specimens ; two of them exhibit the animal of a Vermetus (given 

 in more detail in fig. 19 of the same plate), and one which has 

 a rather contracted mouth to the shell, with what appears to be an 

 Annelide coming out of it. It was the knowledge of this figure 

 that induced me to defer the account of this structure, but the 

 interesting discover)' of Professor Steenstrup leads me to be- 

 lieve that it is a pecidiarity of the species, which has appeared to 

 me to be most probably the case, as the shelly matter which 

 covers up the mouth of the shell is of the same colour, texture, 

 and structure as the rest of the shell, and only differs from it in 

 being less strong and thick. These arched cases must as com- 

 pletely immure the animal as that of Rhizochilus. 



Many species of Ammonites more or less completely contract 

 and arch over the mouth of their shells when the animal has 

 attained its full development ; several specimens with the mouth 

 so contracted are figured by D'Orbigny in his * Paleontologie 

 Francaise,' as Ammonites Martinsii, t. 125 ; A. Braikenridgii, 

 t. 135 (copied PI. XVII. B. fig. 3) ; A. linguiferus, t. 156 ; A. 

 Sauzei, t. 139; A. Bakeria, t. 149; A. hullatus and A. micro- 

 stoma, t. 142, &c. Mr. Owen, in his Lectures on Invertebrata 

 (p. 332), mentions one with the mouth so closed which he ob- 

 served in ]Mr. Pratt's collection. This species is from Normandy, 

 and much resembles A. Bakeria. The mouths of the shells of the 

 genera BaciiUtes and Scaphites are also partially contracted. 



It is to be observed that the Vermeti are attached the greater 

 part of their life ; the Rhizochili only become attached when the 

 mouth is closed, but the Ammonites and Baculites and Scaphites 

 remain free after the mouth is contracted or closed. 



EXPLANATION OF PLATE XVII. B. 



Figs. 1, 2. Rhizochilus antipathicus, from a drawing by Dr. Steenstrup, 



showing the shell with the mouth closed. 

 Fiff. 3. Ammonites Braikenridgii, from D'Orbigny, Ter. Jurass. 1. 135. fig. 5. 

 Fig. 4. Vermetus subcancellatusl , natural size. 

 Figs. 5 & 6. The same, magnified, to show the arch over the mouth. 



