DE. T. DAVIDSON OX EECEXT BEACHIOPODA. 107 



development ends tliere, and ;i true median septum is not produced, uniting tlie piilai- 

 to tlie liinge-plate, as is the case \vitli Zeilleria or Terehratclla proper. The calcareous 

 appendage or loop oi" tlie genus Megerlia follows therefore, in this respect, the modi- 

 fications of the Terehralidce proper ; hut the analogy here ceases, for tlie observations 

 of M. Friele have shown that in these last there exists an entire series of transformations, 

 I'latkliJ'orm, Muijadifoivn, and TerehnUelliform, bearing no analogy with those of 

 Mec/erlia." 



M. Deslongchamps then explains how in subsequent stages the principal laniellic or 

 stems of tlie loop become formed, and that this description of the modifications of the 

 loop must, for the present, l)e restricted to Megerlia trimcata, until those of the other 

 recent and fossil species referred to the genus have been examined. He states that 

 there arc four vascular sinuses in the dorsal valve. 



M. Deslongchamps observes (Eecherchcs sur I'Organisation du Manteau chez les 

 Brachiopodes articules, ]>p. 27, 28) that " at the level of the bifurcation of the median 

 septum the mantle, always lined by tlie pallial apparatus, rises up to join the walls of the 

 visceral cavity, and thence is reflected throughout the length of the arms. Another part 

 passes over tlie lower portion of the median septum, covers the branches connecting this 

 septum to the principal and reflected branches soldered to the brachial appendage and to 

 the transverse basis which unites them, and afterwards forms one membrane in tlie shape 

 of an escutcheon, stretched like the skin of a drum between the free internal parts of 

 these various lamellar apophyses. It there forms the lips of the mouth and of the 

 interbrachial membrane, and is finally united to the corresponding portion of the mantle 

 in the large or ventral valve. Throughout this perambulation the mantle is effectually 

 protected by the pallial apparatus, the spicula of which are almost visible to the naked 

 eye, except on the different branches of the brachial apparatus where they are absent. 

 It results from this arrangement that the spicula form on the escutcheon a small area 

 independent of the rest of the pallial apparatus, and limited in all its circumference by 

 the laminae of the brachial apjiaratus [Plate XX. figs. 18, 19]. ... In the arms and their 

 cii'ri the shape of the spicula is entirely different ; they are arranged exactly like those of 

 the same parts in Terebnttulhia, only their branches are larger and their divisions less 

 numerous. These S2:)icules have almost the aspect of those on the borders of the 

 escutcheon, with this difference, that they are always more elongated in the transverse 

 direction, that is to say perpendicularly to the axis of the length of the canals, and are 

 much more cut out at their edges." 



Dr. Gwyn Jeffreys, in the Ann. & Mag. Nat. Hist, for 1858, ii. pp. 123-4, in referring to 

 Megerlia triuicata, remarks that " Having examined Dr. Turton's specimen in my cabinet, 

 which he is said to have procured from Torbay, and which is referred to in the footnote, 

 p. 3G2, vol. ii. of the ' History of British MoUusca,' I am enabled to state confidently 

 that it belongs to the above species, and not to Terebratula detruncala or dccollata, as 

 therein supposed. M. Collard-Descherres records Terebratula truncata as having been 

 taken on the coast of Finisterrc (Journal de Couchyliologie, tome ii. j). 393), and there is 

 no reason to doubt the possibility of its being a British species." 



Mr. Dall, at p. 130 of his memoir " On a Revision of the Terebratulidte," in the American 



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