A treatise on malacology; or, Shells and shell fish . ot striated, and the wdiole shell has very muchthe aspect of an Anodon. Of the fifth type, connectingthis sub-family to the next, we know nothing more thanwhat has been already stated. As the remaining generaof the Unionidce are neither rich in the number of theirforms, nor abundant in their species, we shall mentionthem wath more conciseness. (266.) According to the views here taken of theHyrin^, we may thus compare the four genera, justdefined, with the circle of the Unionin^. Analogies of the and the Unionin^. Genera of the j„„7^
A treatise on malacology; or, Shells and shell fish . ot striated, and the wdiole shell has very muchthe aspect of an Anodon. Of the fifth type, connectingthis sub-family to the next, we know nothing more thanwhat has been already stated. As the remaining generaof the Unionidce are neither rich in the number of theirforms, nor abundant in their species, we shall mentionthem wath more conciseness. (266.) According to the views here taken of theHyrin^, we may thus compare the four genera, justdefined, with the circle of the Unionin^. Analogies of the and the Unionin^. Genera of the j„„7^„,-„o Genera of the HyriiiLe. * Lnioni/ue. r^. CShell trigonal: posterior side^ zc^ Castalia. J truncate and short. j ^^«^- Hyria. Posterior side lengthened. Unio. ? POTOMIDA, TT ^ (Compressed, broad: bosses not7 t,.......... Hyridella. I striated, retuse; teeth slender.] Lymnadia. C Lengthened oblong; bosses small; i Iridea. Mysci,C. almost obsolete. J 286 SHELLS AND SHELL-FISH. PART The type which we consider unknown, is that whichleads immediately to Iridina, and would consequentlybe deficient in some of the teeth. The other four aresuch obvious representations of their prototypes amongthe Unionin^, that we need not detain the reader byany additional remarks. (267.) Of the iRiDiNiE, only three typical species havebeen yet discovered; and these, we believe, are all from the river Nile. (/. elongata,fig. 60.) The form of thewhole group has been beforestated ; the shell is almost ofequal breadth throughout,with the posterior end nearly,if not quite, as broad as theanterior. This great elongation of the shell must extend,of course, to the animal; and for this reason we admitinto the genus Iridina a singular shell from the sameriver {Iridina Nilotica Fer.), but which has the hingeline only ^^ slightly crenulated at the umbones.* Hereit is that Nature, as it were, is hovering between theconfines of this type and the Anodontince, and plainlyintimates to us whi
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectmollusks, bookyear184
