CARBON" IF EROUSAOB. 09 



ix, Hull, show traces of the broad striated area of that genus. A. jlnl*ll,t, 

 Conrad, from tin- Hamilton group, has also been found to IK- a true I'll /////'/.' From 

 all that is therefore known in regard to the affinities of these extinct shells, we may 

 safely infer that probably all of our Silurian and Devonian species, usually referred 

 to A'-i'-i/fji, especially those of the Hamilton and Cheiming groups, will be found to 

 possess the characters of I'ti i-iniii. or of undescrihed genera. 



It is a fact worthy of note, that \\hile the existing genera of the family l'l> //'//. 

 or .\i-ii-nli, In , form a group at once so natural and distinctly defined that Coucholo- 

 gists meet with little difficulty in deciding what particular forms it should include, 

 the boundaries of the family were not always so sharply marked. For, when we 

 undertake to classify the numerous extinct genera that were introduced, lived out 

 their term, and passed out of existence at various periods during the immense 

 interval of time between the first introduction of this type of life and the present 

 epoch, the case is \ery different ; since \\e tind amongst the vast numbers of fossil 

 speeies, types presenting \arions intermediate gradations between the modern 

 representati\es of this and some of the allied families. For instance, no Concholo- 

 gist could he for a moment in doubt whether any particular species or genus of our 

 existing mollusks belongs more properly to the Ari>-n/i</<r, or to the IMlnitlce. Yet 

 in tracing these two families, by their fossil shells, back into the distant past, we 

 meet \\ith various types presenting such an assemblage of characters as to often 

 render their proper distribution more difficult; especially since we have only the 

 lii, r lit of analogy to guide us in our conclusions respecting the structure of the 

 softer parts of these extinct forms. Some of these peculiar species were formerly 

 referred by many Palaeontologists to the genus Pteten, and by others to Avicvla ; 

 and even now, since the genus Arii-tilnpecten has been established for their recep- 

 tion, authors are by no means agreed whether this genus should be classed with 

 the J '><//', i i</ir or the .!// /////< r. 



Again, no one having even a small amount of conchological knowledge, need be 

 at a loss in deciding to which of the two families, An-lilir or Aviculida?, any of our 

 existing species of bivalves belongs. Yet in passing from group to group of the 

 A f I'l/n , from the recent typical examples through some of the other modem forms, 

 and thence through various extinct types, it will be observed that the hinge plates, 

 or denticles, become more and more oblique, until in some of the Palaeozoic genera, 

 such as Ci/rffntonfii. Vninisniiiii, Dolabra, &c., only a few obscure divisions are to 

 be seen at the remote extremities of the hinge, ranging nearly or quite parallel to 

 the cardinal margin, as in Rnki-r, ////?, /'t,rin in, and other genera apparently belonging 

 to the Ari'fiili'lir. In addition to this, in many of the extinct groups of Ari<-n/i,/,i , 

 such, for instance, as Gryphorhynchm, Myallim, B<ik> i;lli<i, .?., there is as well a 

 de\ eloped cardinal area, as we generally see in the Arcidce ; while this area in 



o remarks on the family Aviculidte, by F. B. Meek, Am. Jour. Sci. and Arts (2d s r.) V..I 

 \.\.\\ II. March, 1864, 46. 



