BRACHIOPODA. 



229 



onstrated, though Noetling mentions {he. cit., p. 368) having seen a specimen 

 showing the internal characters, which convinced him that it could not be 

 a true Porambonites. The nature of these features, however, is not 

 stated. Well preserved interiors of this shell must be of rare occurrence and 

 opportunity is taken therefore of elucidating its structure by a series of trans- 

 verse sections from the beaks forward. It will be seen from these accompany- 

 ing figures that there is a spondylium in each valve, that of the pedicle-valve 

 being at the outset the larger, and continuing further forward than the other. 

 Both are supported by a stout median septal callosity, which, in the brachial 



FlO. 180. 



FIO. ISI. 



no. 162. 



FIO. 163. 



Fio. 164. Fig. 165. Fig. 166. 



Figs. 160-166. Transverse serial sections of a single specimen of Spirifer (NoetUngia) Tsch^kini, allowing tlie 

 structure of the internal apophyses and septa. In all the sections the pedicle-valve (p) is above, 

 the brachial valve (B) below. (c.) 



valve widens and becomes lost in the thickened shell-substance of the muscular 

 region ; that of the pedicle-valve becomes narrowed anteriorly and eventually 

 leaves the spondylium free, or nearly so. These characters are not materially 

 different from those of Porambonites, but a feature of high significance in 

 Spirifer Tscheffkini is the presence of a simple linear cardinal process in the 

 spondylium of the brachial valve. This, with the long, double-areaed hinge- 

 line, the biforate umbones and suggestive external resemblance in contour to 

 Platystrophia, forms a more strongly orthoid combination than has been here- 

 tofore observed among shells with such pronounced pentameroid affinities, and 

 thus makes a more direct connection between Porambonites and the orthoid 

 stock whence they have all been derived. The distinctive generic value of this 

 shell as above expressed may be indicated by the term Noetlingia. 



