BRACHIOPODA. 
199 
anterior slope characterizing the entire group. The internal casts figured by 
OEhlbrt show less highly developed muscular scars and testaceous thickenings, 
a somewhat irregularly divided hinge-plate supported by a median septum and 
slightly developed dental plates. The structure is, in short, very similar to 
that of WiLSONiA, and there appears to be no good reason for dissociating the 
shell from R. Wilsoni, inasmuch as the relative depth and size of muscular scars 
are features of but inferior importance. At all events, the type of structure 
seems to be the same as that which prevails among the earlier representatives 
of Camarotcechia. Bayle’s species, however, bears no little resemblance to 
Sowerby’s Terebratula Stricklandi* of the Wenlock fiiuna, a species finely devel¬ 
oped in the Niagara faunas of Indiana, Illinois and Wisconsin. We have been 
supplied with beautiful internal casts of this species by T. A. Greene, Esq., of 
Milwaukee, obtained from the dolomites in that vicinity, and these show a 
peculiar conformation of the hinge-plate, the lateral components of which are 
divided medially for a portion of their length only, toward the apex the plates 
being curved upward and uniting, thus forming an arched and hollow process 
which is, of course, the representative of the cardinal apophysis in Uncinulus. 
This is a very simple condition of development of this process, and it is inter¬ 
esting to find it so early in the history of the group. The figure of the hinge- 
plate of R. fallaciosa given by (Ehlert (51), is similar to the impression usually 
obtained from internal casts of R. Stricklandi, and it may be found that the 
French species possesses the incipient cardinal process of that shell; in this 
event the term Uncinulina may have a certain value as a distinctive designa¬ 
tion for shells in this condition of development, but for the present it seems 
wiser to include R. Stricklandi within the limits of the genus Uncinulus. 
It is in the fauna of the Lower Helderberg group that the subcuboidal Rhyn- 
chonellas with a highly developed process, attain their characteristic and most 
extreme development. Dr. CEhlert’s figures of this process in Uncinulus sub- 
wilsoni show it to be a simple crescentic apophysis striated longitudinally, but 
in Rhynchonella mutabilis, R. abrupta, R. vellicata, and R. nucleolata. Hall, of the 
Lower Helderberg group, there is usually some evidence of a median division ; 
* Not Rhynchonella Stricklandi (Sow.), Schiiur, which is a Devonian shell. 
