

Suborder 4. 



Podocopa. 



General Characters. Shell without any persistent aperture in front, a 

 of very varying shape and sculpture, but always somewhat flattened below, 

 with the ventral edges of the valves in the oral region conspicuously bent 

 inwards and somewhat bowed, so as to overlap each other, when the shell is 

 closed. Both pairs of antennae well developed and partaking in the movements 

 of the animal, being in some cases adapted for swimming, in other case only 

 for crawling; the posterior ones very unlike those in the 3 preceding suborders, 

 being pronouncedly pediform, geniculate in front, and clawed at the tip. 

 Mandibles, as a rule, well developed and provided with a deflexed 4-articulate 

 palp of moderate size and provided at the base with a movable setiferous 

 lamella. 4 pairs of postoral limbs always present, the anterior ones (maxillae) 

 provided at the base with a large vibratory plate and terminating in 4 densely 

 crowded and more or less digitiform setiferous lobes, the outermost of which 

 represents the palp. The next pair of limbs in some cases subservient to 

 mastication and having the palp (endopodite) imperfectly developed, thus more 

 properly termed maxillipeds, in other cases however pronouncedly pediform, 

 like the 2 succeeding pairs. Caudal rami, when perfectly developed, forming 2 

 slender and very mobile pieces armed at the tip with 2 claws only, in many 

 cases however much reduced in size and apparently immobile. Compound 

 eyes wanting, but in most cases an ocellus, simple or bipartite, may be found 

 to exist. No frontal tentacle nor any trace of a heart present. Intestine divided 

 by a mediate constriction into 2 well defined compartiments, the anterior of 

 which may be provided with 2 more or less developed lateral coeca. Genital 

 organs of rather varying structure. Copulative appendages of male symme- 

 trical and often very complex. 



Remarks. This suborder proposed by the present author in 1865, is 

 very natural one, exhibiting a number of well marked distinguishing characters 

 derived both from the shell and from the enclosed body. It has also been 

 approved by all subsequent authors, though its limits were somewhat altered 



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