SAXICAVA 



Pholeobius includes as distinct species of the same genus 

 the Solen minutus of Montagu, and the Mytilm rugosus 

 of Linn, will also be readily admitted; now the former of 

 these is Hiatella arcfica of Lam, and Turton, and the 

 IditiGY Scuvicava rugosa i)i the same authors; thus all the 

 six genera are reduced to one by Dr. Leach, whose 

 authority is indisputably very great in such matters; 

 we do not, however, propose to our readers to take it as 

 conclusive, but will state that we possess, as Dr. Leach 

 also did, a series of specimens, the young ones of which 

 are more regular in shape, and more strongly spinose 

 than the older, and are to all intents and purposes Hia- 

 tella arctica, or Solen minutus^ and the older specimens, 

 losing the strongly marked double rows of spines, though 

 always retaining indications of them, and assuming a 

 much less regular form, become characteristic speci- 

 mens of Saxicava rugosa: the hinge teeth of the younger 

 specimens may be advanced as an argument against the 

 identity of these shells, it is, however, well known that 

 in many shells, particularly those that are irregular, the 

 teeth become obsolete with age : thus, if the hinge teeth, 

 the general form of the shells, or the double row of spines 

 cannot be depended upon as generic distinctions, the 

 Lamarckian genera Hiatella and Saxicava, and his Solen 

 minutus merge into one : to show that the shells described 

 as distinct species under either of these generic names are 

 identical, is not important in the present work; it is there- 

 fore sufiicient to observe, that in all irregular shells, 

 that are either found attached to, or imbedded in rocks, 

 corals, roots of sea- weeds, &c. the general form cannot 

 be taken as a character; and we believe the Mytilus 

 2)ra-cisus, and several of the Saxicavce described by Lamarck 

 and Turton, to be merely variations of S. rugosa, than 

 which there is perhaps no shell more subject to variety in 

 form. 



Shell transverse, irregular, generally oblong, in- 

 equilateral, rather inequivalve, generally gaping in front, 

 sometimes at both ends. Ligament external. Muscular 

 impressions two, lateral impression of the muscle by 

 which the ligament is attached, irregularly interrupted, 

 without any sinus. Teeth in the young shells small, obtuse, 

 generally indistinct, in the old shells obsolete. 



