86 SAXICAVID^K. 



of shape between this genus and Tapes; but the shell 

 of Venerupis is regularly cancellated, while that of Tapes 

 is nearly smooth or marked only by concentric flattened 

 ribs and obscure or microscopical longitudinal striae. 

 Perhaps Venerupis is here scarcely in its place. It is 

 impossible to make a linear or graduating arrangement. 

 An oak tree in the course of its growth will have many 

 interlacing boughs, and will spread out : so with the 

 system of natural history in passing through successive 

 stages of development. The Venerupes occupy holes 

 made by Saxicava, or attach themselves by byssal 

 threads to rocks and other substances. The genus does 

 not claim a greater antiquity than the miocene period. 



Venerupis Irus*, Linne. 



Donax Irus, Linn. S. N. p. 1128. V. irus, F. & H. i. p. 156, pi. vii. f. 1-3, 

 and (animal) pi. G. f. 2. 



Body white with a pinkish tinge : tubes slender, unequal in 

 length, pellucid, speckled with flake-white, diverging near the 

 extremities, which are of a pink colour ; longer cirri of the 

 orifice erect and feathered, shorter ones reflected and plain ; 

 retractile valve of excretal tube conspicuous. 



Shell oblong, compressed, slightly gaping at the posterior 

 end but in no other part, solid, opaque, and usually lustre- 

 less : sculpture, 15-20 thin laminar concentric ridges, which 

 become broader and foliaceous towards each end of the shell ; 

 these ridges and their interstices are crossed by numerous fine 

 longitudinal striae, radiating from the beaks ; the surface is 

 also covered with minute close-set transverse striae : colour 

 pale yellowish-white, with sometimes (especially in the young) 

 a stain of reddish-brown or purple on the umbonal area and 

 posterior side : epidermis thin and seldom visible : margins 

 rounded or obtusely angular on the anterior side, usually 

 straight in front, truncated or wedge-shaped on the posterior 

 side, which is at least twice as large as the opposite side, more 

 or less straight behind, with an abrupt slope from the beaks 



* The name of a beggar in the Odyssey. 



