102 SYNOPSIS OF THE CHARACTERS OF THE 



about twenty-six unequal, rounded ridges ; ears radiated with three or four similar ridges ; the ears, and some- 

 times the margin of the valves, are sharply striated concentrically. 



This curious little shell resembles the M. decussata of the Oolite in shape, having a distinct, but small ear 

 on the anterior side. It occurs in great abundance in company with the P. simplex, Phil., which it much re- 

 sembles, but which is easily known from the present shell by its smooth, equal ears, finer stride, and lengthened, 

 oblique form. Length three lines, width three lines. 



BRACHIOPODA. 



Before entering on the Brachiopoda I shall give a brief outline of what has been done by the principal 

 writers on the subject. 



Cuvier included in his Brachiopoda only the genera. Linffula,Terebratula, Spirifer, Thecidea, Orbiciila, 

 and Crania. 



Lamarck removed Crania from the Brachiopoda to his family Rudistes, in which he also placed Calceola 

 and Discina; he included only in the Brachiopoda the genera Orbicida, Terebratula, and Lingula. 



De Blainville forms his order Palliobranchiata of the genera Lingida, Terebratula, Strophomena, Dian- 

 chora, Thecidea, Phujiontoma, Podopsis, Orbicula, and Crania. This author, it will be observed, admits the 

 genus Strophomena {Productus), but also arranges with ihera. Dianchora, Podopsis, and Plagiostoma, genera 

 which almost every other author agrees to have little or no affinity with them. 



Deshayes recommends the suppression of the genus Spirifer, considering, with many others, that the spiral ap- 

 pendages are the spiral arms of the animal, common to all the Brachiopoda ; hence he believed that genus not to 

 possess any peculiar generic character, and therefore places all the Spir-ifej-s either in the genus Terebratula 

 or Producta, according to whether the foramen in the beak of the large valve be distinctly visible or otherwise. 

 Leaving out of consideration what appears to be the primary error in this view, namely, the considering the 

 spiral appendages of Spirifer as the spiral arms of the animal, a great source of inconvenience in this arrange- 

 ment is, that nearly allied species, and sometimes even two specimens of the same species, must be separated 

 into two distinct genera. 



o 



Von Buch, in his Memoir, " Uber die Terebrateln" (1834), produced the most remarkable and valuable 

 arrangement of this tribe which we possess. His method is a dichotomous one, somewhat resembling Dr. Fle- 

 ming's system. He first divides the Brachiopoda into those which are attached by the margin, and those at- 

 tached by the lower side of the shell. The first group he then divides into those which have one valve perfo- 

 rated, and those having neither valve perforated. The former he afterwai'ds subdivides into those which have 

 the perforation separated by a deltideum from the hinge-line, including, under the name of Terebratula, the 

 genera Atrypa, StrUjocephalus, Uncites, Pentamerus, and Mec/as^, and those which have a triangular foramen, 

 the base of which rests on the hinge-line, including, under the name oiDelthyris, the genera Spirifer, Orthis, 

 Ctjrtia, and Gypidea. Those having neither valve perforated, he separates into such as have a large cardinal 

 area, including only Calceola; and such as have no cardinal area, being Lej)tcena (^Producta, Strophomena). 

 His second great division, those attached by the lower side, is divided into that having the lower vah-e pierced 

 for attachment, containing Orbicula, and secondly that having the lower valve entire, and attached by its whole 

 face, including Crania. 



* Professor PhilHps translating this table in his " Palaeozoic FossUs," places Orthis in this division instead of 

 the next. 



