262 Dr. J. Allan Thomson — The genus Bouchardia. 



Remarks on the genxts Bouchardia. 



Since an external form similar to that of Bouchardia may be 

 combined with a more advanced loop, it is necessary before a given 

 species can be certainly referred to the genus to have some knowledge 

 of the interior arrangements. The loop is known only in the recent 

 species B. rosea, and consists of two "anchor-shaped disconnected 

 curved lamellae " fixed to the posterior end of a high septum. These 

 lamellae resemble those of the ascending portion of the loop of Magas, 

 and in both genera they are disconnected, and not united to form 

 a ring as in Magadina and in the Magadiniform and pre-Magadiniform 

 stages of Terelratella.^ The descending branches of the loop, which 

 are complete in Magas and Magadina, are totally absent in B. rosea. 

 Beecher has compared the early pre-Magadiniform stages of Tere- 

 hratella with the adult loop of Bouchardia, but there is this important 

 difference, that in the young of Terelratella the growth of the 

 descending branches commences before that of the ascending 

 branches, and there is never a stage in which the ascending branches 

 do not form a complete ring or hood on the septum. 



If Bouchardia is correctly placed in the MagellanincB, B. rosea must 

 be looked upon as a retrograde species, descended from a form 

 possessing a complete ring on the septum and incomplete descending 

 branches, and now attaining a less instead of a greater calcification 

 of the loop than its forerunners. If this view is correct, the loops 

 of the fossil species of Bouchardia may be expected to show a greater 

 calcification than exists in B. rosea. This expectation is not realized 

 in B. minima, for numerous interiors of this species are available, 

 but show no trace at all of a loop except a slight swelling on the 

 posterior end of the septum which closely resembles the first stage of 

 the hood in the young of Terehratella rulicunda. If this is a correct 

 homology, then Bouchardia minima represents a still earlier loop stage 

 than B. rosea, but is apparently also degenerate in that the descending 

 branches are not calcified, since these appear first in the Terebratelli- 

 form development. The septum does not unite with the cardinalia 

 in B. minima, which supports the view that its brachidium is in 

 a less advanced stage than that of B. rosea. 



Buckman states that many of the Antarctic Bouchardi(B examined 

 by him were in such condition as to show the internal characters, 

 but, unfortunately for the purposes of this discussion, he has given 

 no further information than may be gleaned from an enlarged view 

 of the interior of B. angusta. The characters of the cardinalia seem 

 essentially similar to those of B. minima in the smaller of the two 

 figures given, but little can be made of the nature of the loop if any 

 exists. The case is still worse for B. %iUeli, von Ihering, for von 

 Ihering's figure is far from satisfactory. The interiors of the other 

 species ascribed to Bouchardia have not been described or figured. 



Von Ihering in 1907 argued from the then known distribution of 

 Bouchardia only in the Salamancan and Patagonian of Patagonia and 



^ Cf. P. Fischer & D. P. Oehlert, " Mission scientifique du Cap Horn 

 (1882-3) : Brachiopodes " : Bull. See. Hist. Nat. d'Autun, t. v, pp. 254-334, 

 1892. J. A. Thomson, ' ' Additions to the knowledge of the Eecent Brachiopoda 

 of New Zealand"*: Trans. N.Z. Inst., vol. xlvii, pp. 404-9, 1915. 



