24 MAZATLAy BIVALVES 



Genus SPH^NIA, Tiirton. 



For Mouograpli of tlii^ genus, witli amended generic characters, 

 see A. Adams in Proc. Zool. Soc. 1850, p. 86. See also Forbes 

 <f- mail. Br. Mol. vol. 1. p. 189—193 -.—Clarh Br. Mar. Test, 

 Moll p. 150, 



35. SPH.SNIA FEAGILIS, «. S. 



S. animali in cryptis latibulante, ergo varie distoi^to ; testa 

 parva, tenui, subnacred, vix rugose striatd ; epidermidefusco- 

 vlrente copiose indutd, rugarum increscentium concentricarum 

 plena, postice in sipJione longa porrecta : parte posticd plus 

 mimcsve subcarinaid ; valvd sinistra dente ligamentum ferente, 

 plus minusve seuprolongatd seu extante; dextrd alveo conveniente. 

 nonnunquam denticulo subextanie : impressionibus muscularibus 

 subrotundatis, sinu pallii lato, rotundato, liaud alto. 



It is surprising kow mncli of the very minute description of 

 S. BLnghami given in Forbes Sf Sanl. Br. Moll. i. 191-2, applies 

 exactly to individiials of this species. Indeed, if young speci- 

 mens of the two were mixed together, I should hardly know 

 any sufficient ground of specific distinction, except in the texture 

 which is more nacreous, and the paUial sinus which is broad, 

 though shallow. The yomag shells can sometimes be told from 

 those of Saxicava arctica only by the hinge, as in Biughami ; 

 and there is often seen the Little denticle by the ligament pit 

 noticed by Turton, not Hanley, and conspicuous in .Aoung 

 shells of Spha'uia Binghami in my possession, nesthng in cre- 

 vices of liuiestone dredged off Weymouth. Like other nestlers 

 (unlike the true borers, which are moderately constant in form) 

 it is extremely iiTcgular. Many well characterized species 

 might be made out of extreme forms ; but ujifortimatel.y 

 for the lovers of multiplication, individuals were sufficiently 

 numerous to supply many connecting links. The normal state 

 appears to be not very inaqiiilatcral and tolerably ^veU roimded : 

 the shell is then shaped somewhat like Psammobia : but it is 

 generally more or less produced, when the posterior portion 

 becomes marked off by an angle, in very long specimens 

 amoimting to a keel, sometimes with a trace of a double one. 

 \Vlien it lives in dead Balani &c., it becomes very short, inflated 

 and gibbous, resembling Corbula or sometimes Neajra. The 

 ligamental plate then becomes narrow, projecting andsiuuated. 

 more like the tooth of Mya. These variations are seen in the 



