CLASSIFICATION OF THE BRACHIOPODA. 57 



Very remarkable differences in the vascular impressions left by the mantle on the inner 

 surface of the shell have been observed, and this subject deserves much more minute in- 

 vestigation, in order to be used as a substantial character in the distinction of families. 



It now remains for us to examine what results may be obtained from the characters 

 afforded by the labial appendages or cirrated arms, the most important portions of the 

 animal in the Brachiopoda ; and I have little doubt that in them will be found the best 

 character for distinguishing the great families as well as most of the genera -^ but in order 

 to better appreciate some of these dissimilarities, we will successively and briefly pass in 

 review the principal modifications they assume in the different families, reserving all details 

 connected with the genera for that portion of the introduction which treats of them in 

 particular. 



1. In the Terebratulid^ the cirrated arms^ are variously twisted or folded upon 

 themselves, and connected, to a greater or lesser extent, by a membrane, becoming free only 

 at their spiral ends.^ These labial appendages are always more or less supported by a 

 calcified lamellar process, which assumes various shapes, but more commonly that of a 

 loop, which is either simply fixed to the hinge plate, or likewise so to a medial septum in 

 the dorsal valve. From differences observable in the shape and character of this kind of 

 internal skeleton, the family may be readily and conveniently sub-divided into the follow- 

 ing sections or sub-sections, Terehratula, TerehratuUna, Waldheimia, Terebratella, Megerlia, 

 Kraussia, Magas, Bouchardia, Morrisia, and Argiope. 



2. Stringocephalus has been provisionally placed in a sub-family, of which it is 

 the only member, on account of its peculiar organisation ; the exact character of its oral 

 appendages has not hitherto been completely elucidated, but from the discoveries made by 



1 M. d'Orbigny justly attaches great importance to characters derived from the arms in the classi- 

 fication of the Ordeii. 



2 Commonly described as ''ciliated" arras; but the term cilia ought to be restricted to the micro- 

 scopic vibratile organs, described by Dr. Grant and Prof. Sharpey. 



' Baron von Buch mentions that Otto Frederic MUller having dredged from the lake of Drsebach, in 

 Norway, a number of Terebratulce (probably belonging to Rhynchonella psittacea^, and placed them in a 

 glass of water, he observed that they gracefully extended their spirally coiled arms. Professor Owen and 

 M. Phillipi appear not to have watched the actions of any Brachiopoda in the living state; but from the 

 examination of preserved specimens, they have arrived at the conclusion, that they were able to unfold the 

 ^jiral portion of their arms. Professor Forbes, who has frequently dredged living Terebratulce on the 

 coasts of Scotland, and also in the Mediterranean, when describing the animal of Terebratitlina caput- 

 serpentis ('History of British MoUusca'), states that the arms themselves cannot be protruded. The exact 

 resemblance of these arms to the calcareous spiral appendages of Atrypa and Spirifer, led me to doubt the 

 accuracy of the observations made nearly a century ago, by the excellent naturalist quoted by Baron 

 V. Buch, and to suppose that the canal and muscular fibres of the oral arms might be intended to inject 

 the cirri, and not to protrude the arms themselves ; but I may have been mistaken in my suppositions. 

 Through the kindness of Mr. Cuming, Mr. Woodward and myself were enabled to examine these 

 beautiful appendages in the R. nigricans, dredged alive by Mr. F. J. Evans, R.N., in Foveaux Straits, 

 about five miles N.E. of Ruapuke Island, New Zealand (19 fatlioms) ; and after having forcibly extended 

 the arms, we were able to count the coils, which numbered eight or nine. 



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