Family XVI. SOLE'NID^E, Latreille. 



BODY elongated in a transverse direction : mantle closed in 

 front, with its borders adhering together, open at the anterior 

 end for the passage of a foot, and forming at the posterior end 

 two conical tubes or siphons of different lengths, which are 

 more or less enclosed in a common sheath : gills two on each 

 side, long and narrow : palps corresponding with the gills in 

 number and position, long, slender, and triangular : foot large 

 and muscular, adapted for burrowing in sand. 



SHELL shaped like the body, equivalve, open or gaping at 

 both ends: epidermis strong and persistent, overlapping the 

 front or ventral edges of the shell : beaks small : ligament ex- 

 ternal : hinge strengthened inside by a ridge : teeth consisting 

 of one or two thorn -like cardinals in each valve, which are 

 erect, curved, and interlock ; laterals partly recumbent, in 

 some cases rudimentary or wanting : muscular scars irregular : 

 pallial scar sinuated. 



This and the succeeding families of marine Conchifera 

 differ from those described in the second volume in 

 having the mantle more or less closed in front. Pro- 

 fessor Oken imagined that, in a biological point of view, 

 they typify the Nudibranohs and Salpse; but he gave 

 no reason for this fanciful analogy. Although the 

 Solenida appear at first sight to constitute a natural 

 and simple group, it will be found to comprise certain 

 forms which connect it with, other families. This resem- 

 blance has probably misled some systematists, and in- 

 duced them to associate with Solen such very dissimilar 

 genera as Psammobia, Lutraria, Panoptea, and Mya. 

 The structure of the hinge, however, will always serve 

 to distinguish any one of them from the rest. 



Dr. Carpenter says that the external layer of the 

 shells in the present family is composed of cells which 



VOL. III. B 



