THE BRITISH FOSSIL BRACHIOPODA. 291 



add a chapter to my General Introduction, " On the Intimate Structure of the Shell of the 

 Brachiopoda," with illustrations. To this proposal he at once acquiesced and devoted 

 much time and labour to the investigation, and I must refer the student to that memoir 

 and to its plates for more ample details than I can at present impart. The structure of 

 the shell has been shown by Dr. Carpenter, Professor King, 1 Dr. Gratiolet, 2 E. Deslong- 

 champs, 3 Van Bemmelen, 4 Mr. John Young, 5 myself, and others, 6 to be generally distinct 

 from that of the Lamellibranchiata and Gasteropoda. Dr. Carpenter stated, in my first 

 volume, that in the shell of the Brachiopoda there is not that distinction between outer 

 and inner layers, either in structure or mode of growth, which prevails among the ordinary 

 Bivalves, and that it seems obvious, both from the nature and form of the shell-substance, 

 and the mode in which it is extended, that the whole thickness of the Brachiopod shell 

 corresponds with the outer layer only of the Lamellibranch. He added that he has, how- 

 ever, occasionally met with a second layer in recent Terebratulte within the earlier formed 

 portion of the shell, but confined only to a part, instead of extending beyond it. Also that in 

 the genera of species which have their shell perforated by canals, these canals differ in size, 

 and are situated at variable distances from each other. 7 They make their appearance in the 



Crustacea, and Echinodermata," 'Annals and Mag. of Nat. Hist.,' vol. xii, p. 377, 1843. On account of 

 his valuable researches the Royal Society awarded to Dr. Carpenter one of its Royal Medals. 



" On the Microscopic Structure of Shells," ' Report of the Fourteenth Meeting of the British Associa- 

 tion for the Advancement of Science,' for year 1844, p. 1, and in 'Report Brit. Assoc' for 1847, p. 93. 



Article " Shell," ' Cyclopaedia of Anatomy and Physiology,' 1850. 



"Intimate Structure of Shells of Brachiopoda" (Davidson's 'Introduction to British Fossil Brachiopoda,' 

 1853). 



"On a Peculiar Arrangement of the Sanguiferous System in Terebratula," ' Proc. Royal Soc. London,' 

 vol. vii, p. 32, 1854. 



" On the Shell Structure of Spirifer cuspidatus," ' Geol. Mag.,' 1867. 



1 "On some Perforated Palaeozoic Spiriferidse," 'Geol. Mag.,' vol. iv, p. 253, 1867. 



2 " Recherches pour servir a l'Histoire des Brachiopodes," ' Journal de Conchyliologie,' t. viii, p. 49, 

 2nd ser., 1860. 



"On the Histology of the Test of the Class Palliobranchiata," 'Trans. Royal Irish Acad.,' vol. xxiv, 

 p. 439, 1871. Prof. King's important observations have thrown much light upon the intimate structure of 

 the shell, and should be studied. 



3 At p. 17, pi. viii of his ' Paleontologie Francaise, Brachiopodes Jurassiques,' t. vi, 1862, Mr. E. 

 Deslongchamps describes and figures the shell-structure of the Brachiopoda. 



4 "Over den bouw der Schelpen van Brachiopoden en Chitonen, 1882 ; and Untersuchungen iiber den 

 anatomischen und histologischen Bau der Brachiopoda Testicardinia, 1883," in the ' Jenaische Zeitschrift 

 fur Naturwissenschaft,' Band xvi, 1883, and 'Annals and Mag. of Nat. Hist.' for May, p. 379, 1883. 



5 Davidson's ' Carb. Supp.,' vol. iv, p. 296. The shell-structure of Rhynckopora, Orthis, Productus, 

 Chonetes, &c, has been kindly and ably worked out by Mr. John Young for the pages of my Monograph. 



6 See Bowerbank's " Observations on the Structure of the Shells of the Molluscous and Conchiferous 

 Animals," 'Transactions of the Microscopical Society,' i, p. 123, 1844. 



7 Both Morse and Kowalevsky describe the formation of the shell. Kowalevsky referring to the larva 

 of Cistella cistellula prior to the formation of the shell, says, "The shell then consists of a chitinous 

 layer and calcareous prisms, which cease to be deposited at a certain distance from the margin. It is 



39 



