CLASSIFICATION OF THE BRACHIOPODA. 49 



Lingula, Orbicula, Crania, Calceola, Thecidea, Terebratula, Spirifer, and Productiis. The 

 second six, viz. : Terebratula, Spirifer, Orthis, Productus, Lingula, and Thecidea. 

 In 1852, Professor M'Coy divides the Palliobranchiata into two orders:' 



1st Order. Rudistes (Lam.) contains three famihes : — \, Tliecidece ; 2, Caprinidee ; 



3, Padiolidce. 



2d Order into eleven families: — 1, Craniadce ; 2, Orbiculidce ; 3, Tercbratulida; ; 



4, Magasidce ; 5, Spiriferidce ; 6, Uncitidcs ; 7, RhyncJionellidce ; 8, Orthisida ; 9, Pro- 

 ductidcB ; 10, Calceolida ; 11, Lingulida. 



Professor M'Coy has fallen mto the same mistake as M. d'Orbigny, viz. by placing 

 Thecidium among the Rudistes. In the 2d Order his 4th and 6th families may be 

 dispensed with, the 4th belonging to the Terebratulida, the 6th to the Spiriferidce. 



From the above brief summary it is evident that the tendencies of some have been to 

 multiply, others to reduce, the number of genera ; this fluctuation of opinion proceeds 

 from the different relative value or importance attributed to certain characters which are 

 by some considered generic, by others only specific. Thus, for example. Prof. Quenstedt 

 divides his genus 7^ere^r«^2^/a into 1, Bicornes ; 2, Calcispirce ; 2>, Annulifene ; ^, Lori- 

 catce ; 5, Cinctce ; 6, Impressa ; 7, Nucleate ; 8, Triplicata ; 9, SpiriferincB. Now, 

 in my opinion, as well as in that of many other Palaeontologists, his Terebratuljj 

 Calcispir^ {T. prisca and prunum) and his Terebratula spirieerina {T. concentrica, 

 tmnida, ferita, &c.) from possessing internal spires for the support of the cirrated arms, 

 similar in essential or family character to those of Spirifer, would be much more 

 natm^ally and properly classed under the last-named genus, and the objection to placing 

 in the same section or family such shells or animals as Ter. vitrea, B. psittacea, A. prisca 

 and S. concentrica, is too obvious to demand any lengthened explanations ; for both the 

 dispositions of the oral processes, and other details of the animal economy, are essentially 

 dissimilar, and therefore could not possibly be confounded under a single denomination ; 

 otherwise the drawing up of a uniform and clear diagnosis would be impossible, and thus 

 lead to very serious practical inconveniences. Those who have devoted serious attention to 

 the external and internal characters of these shells, have come to the conclusion that 

 the class is now sufficiently investigated to be susceptible of subdivision into natural 

 groups or families, and these again into genera. Thus, for example, we are acquainted 

 with upwards of a hundred species of Terebratulce, presenting exactly the same internal 

 dispositions, namely, a short simply-attached loop supporting similarly disposed cirrated 

 arms ; to such a group the same generic appellation is natural and proper ; but not 

 if likewise made to include another equally numerous series of species, in which, besides 

 differences in the external and shell structure, we find free extensile spiral arms {Bhyn- 

 chonella), supported only at their origin by two slender curved lamellae. Still, according 



' British Palaeozoic Fossils, part '2, p. 186, 18.52. 



