GASTEROPODA. 



379 



Order VII. SCUTIKRANCHIATA* 



(Cuv.) 



Syn* Cervicobranches, Blain. ; Ckisjno- 

 branches, Blain. ; Gast. Dermobranches, Dum.; 

 G. Trachelipodes, Lam. 



Fig. 176. 



In this order the structure of the branchiae 

 is analogous to what has been described in the 

 Pectinibranchiata ; but the shell, which in the 

 latter was always turbinated, in the Scutibran- 

 chiata is a mere shield, in which the indications 

 of a spire are very slight or totally deficient. 

 There is never an operculum. The organs of 

 both sexes are united in every individual, but 

 there is no necessity for copulation, each ani- 

 mal being self-impregnating. The species are 

 all aquatic. 

 1st Sub-order, Anthopliora.\ 



1st Fam. Haliotis, jig. 176. 

 2d Sub-order, CalyptracidtP,\ Lam. 



* Scutum, a shield. 

 t Avfloj, a flower ; $1?* 

 a covering. 



to carry. 



2d Fam. Capulus* 

 3d Sub-order, Heteropoda\ Nucleobranches, 



Blainville. 

 3d Fam. Pterotrachea, Jig. 177. 



Order VIII. CYCLOBRANCHIATA, 



(Cur.) 



Syn. Dermobranches, Dum. ; Gast . Phylli- 

 diens, Lam. ; Gast. Chismobranches, Blain. 



In this order the branchiae are arranged 

 under the margin of the mantle around the 

 circumference of the body ; the shell is a 

 simple shield, either composed of one piece, 

 which is never turbinated, or else made up of 

 several divisions. They are all hermaphrodite 

 and self-impregnating. 



1st Sub-order, Chismobranchiata, Blain.; Cy- 

 clobranchiata, Goldfuss. 



1st Fam. Patella. 

 2d Sub-order, Polyplaxiphora,\ Blain. 



2d Fara. Oscabrion. 



Cuvier detaches the genera Vermetus, Magi- 

 lus, and Siliquaria from the Pectinibranchiata 

 on account of the irregular form of their shell, 

 which is only spiral at its commencement, and 

 is usually firmly attached to some foreign body, 

 a circumstance which involves as a necessary 

 consequence the hermaphrodite type of the 

 sexual organs, so that these genera are self- 

 impregnating. He has, therefore, arranged 

 them in a separate order, to which he applies 

 the name of Tubulibranchiata. 



Tegumentary system. The skin which in- 

 vests the Gasteropoda varies exceedingly in 

 texture, not only in different species but in dif- 

 ferent parts of the same animal ; its structure 

 being modified by a variety of circumstances 

 connected with the habits of the creature, the 

 presence or absence of a calcareous covering, or 

 the mode of respiration. In the naked Gaste- 

 ropods, especially in the terrestrial species, it is 

 thick and rugose, serving as a protection against 

 the vicissitudes consequent upon the changeable 

 medium which they inhabit. In such as are 

 aquatic the integument is proportionably thin- 

 ner, and its surface more smooth and even ; in 

 both, however, it differs much in texture in dif- 

 ferent parts of the body ; thus in the dermo- 

 branchiate species it becomes attenuated into a 

 thin film, where it invests the vascular appen- 

 dages subservient to respiration, and such por- 

 tions as cover the organs of sense assume a 

 transparency and delicacy adapted to the sen- 

 sibility of the parts beneath. In those orders 

 which are provided with shells, the integument 

 which protects such parts of the body as are 

 exposed when the animal partially emerges 

 from its abode, is thick and spongy, and very 

 different from the thin fibrous membrane which 

 invests the mass of viscera contained within 

 the shell. We are led by various circum- 

 stances to presume that the skin of all the 

 Gasteropods is in structure essentially ana- 

 logous to that of higher animals, and in de- 



* Many of the Capuloid Gasteropods are thought 

 by Cuvier to be diacious. 



t ETtpoc, different; irovf, foot. 

 $ nXuf, many; wXa, a scale ; <J*?, to carry. 

 2 c 2 



