129 



II. GASTROCH^NIDiE. 



We have seen that several of the mollusks of the pre- 

 ceding family secrete a testaceous tube, which lines their 

 habitations and protects their siphons. This character was 

 laid undue stress upon by Lamarck, who united with the 

 tube-forming- species of Pholadidce the genera Fisfulana, 

 Clavagella and Aspergillum, and constituted thus his 

 family of Tuhicolce. This family was afterwards reformed 

 by Deshayes, and restricted to the three last-named La- 

 marckian genera, which were retained by him as Asjyer- 

 gillum^ Clavagella.^ and Gasirochana. The tube-making 

 character is, however, as unessential here as it is in the 

 Pholadida; and, as we shall see presently, the genus Saxi- 

 cax>a^ which is always free, must take rank next after and 

 along with GastrocheEna, whilst Petricola, and probably 

 Venerupis, have strong claims to a similar position. 



The animals of this family are oblong or claviform, and 

 often provided with very long siphons, united almost to 

 their extremities, where their orifices are ornamented with 

 cirrhi. The mantle is closed in front, except a small open- 

 ing for the passage of a very small digitiform foot, very 

 different from that of the Pholas tribe. The margin of the 

 mantle around this opening is plain. The shell is equi- 

 valve and often gaping, with valves often very inequi- 

 lateral, united by a simple rudiment, or in some cases a 

 toothed hinge, often variable even in the species of a single 

 genus. They have no spoon-shaped apophysis under the 

 beaks, nor accessory plates behind them. A calcareous 



VOL. I. s 



