CLASSIFICATION OF THE BRACHIOPODA. 59 



of several species, but no developed calcified process existed for their support, and the arms 

 were perhaps supported in a somewhat similar manner to what we observe in the Craniadce 

 and DiscinidcB. 



8. Nothing is known regarding the arms in Calceola, a genus completely anomalous 

 in the class. 



9. The labial appendages in the Craniadce, Discinida, and Lingulida, are fleshy and 

 spirally coiled. From this rapid examination it seems evident that the best characters 

 for the subdivision of the class may be derived from the shape of the arms and their calci- 

 fied supports ; and by taking into account other peculiarities which accompany the modifi- 

 cations above described, one may hope to arrive in time at a rational arrangement of the 

 numberless forms comprised in the Palliobranchiata. 



The geological and vertical range of some of the genera and species has to a certain 

 extent been alluded to by several authors, but M. d'Orbigny claims the merit of having 

 first endeavoured to arrange the general distribution in a tabular shape.^ He divides the 

 sedimentary strata into 27 epochs,^ and therein locates the genera, taking care to illustrate 

 his views at the same time as to the numerical development of species by peculiar signs. 

 This, like all similar attempts, must be considered as merely approximative, since fresh dis- 

 coveries are every day liable to modify the limits and numerical importance we may assign 

 to the genera, since Palaeontologists are not yet able to place all the Palaeozoic species with 

 certainty in their proper places. So much confusion likewise exists in the synonyms 

 that it would require much time and investigation to settle, if even possible, the true amount 

 of known species. We differ from the learned author of the ' Paleontologie Francaise ' in 

 certain details regarding the first appearance and disappearance of some of the genera; and 

 in the Table accompanying this introduction, I have endeavoured to mark the extent of 

 development at present known derived from positive examination, and under each genus 

 have only mentioned a few examples which I had thoroughly examined and known to 

 belong to the group ; the principal defect in the 'Prodrome' lately published by the French 

 author above mentioned, as well as in all similar catalogues, consisting in the necessity of 

 forcing into sections a number of species with whose internal character the compiler is 

 necessarily unacquainted. 



Thus, for example, M. d'Orbigny characterises his genus Atrypa (not of Dalman), 

 as a shell dejmved of perforation for the passage of a muscular pedicle, with free extensile 

 fleshy arms, supported only at their origin by two short curved lamellcB, in every respect 

 similar to those of Rhynchonella, from which the author states it to be distinguished simply 

 by the {often very questionable) want of a foramen. He gives a list of 188 species which 

 are stated to agree with his diagnosis, and consequently members of his section. Now 

 let any one examine this list with care, and he will soon be convinced of the dissimilarity 

 of the internal organisations there assembled ; and I may boldly assert that a number of the 



^ Cours Elementaire de Paleontologie et de Geologie Stratigraphiques, tableau ix, 1852. 

 2 The exactness of such a system requires still to be proved. 



