BRACHIOPODA. 17 



Mr. Davidson has referred two Devonian species to Spiriferina, 8. cristata 

 Schlotheini, var. odoplicata, and S. insculpta, Phillips ( ? ), both of Avhich are 

 described as having a punctate structure. It is not known, however, whether 

 in these early forms the loop has attained its ultimate development; Ave might 

 expect to find it with its lateral branches discrete as in the true Spirifers. 



The species of this septate section have, so fiir as known, the surface of the 

 concentric lamellae covered with fine radiating striae which were evidently not 

 continued into spines or fimbriae. Among the forms which are referred to 

 the genus Spiriferina nearly every variation of surface ornament is to be found 

 except this. The Carboniferous species, like S. Kentuckiensis and S. solidirostris, 

 which resemble very closely in other respects these septate lamellose Spirifers, 



are fimbriated. 



•J 



2. Aseptati. Those without a median septum in the pedicle-valve. These 

 species are more abundantly plicated, often much more extended on the hinge 

 than in the septate group. The lamellae are without radial striations. The 

 Aseptati group themselves naturally about two type-forms, the first, (a), Spirifer 

 mucronatus, Conrad, an alate, maltijjlicate shell with a single low plication in 

 the sinus and a corresponding depression on the median fold ; the other, (b), 

 Spirifer submucronatus, Hall, in which the fold and sinus are not plicate. 



Of these subdivisions the latter was the first to appear in the American 

 Palaeozoic, and is represented by S. submucronatus, and S. Cumberlandicz, Hall, of 

 the Oriskany sandstone of Maryland, S. macrus, Hall, S. gregarius, Clapp, and 

 an undescribed species from the Upper Helderberg group. Spirifer gregarius 

 is of interest in having a high area, a rather short hinge, and in assuming some of 

 the characters of the group of the Ostiolati in its internal umbonal callosities. 



The Mucronatus-type does not appear earlier than the Hamilton fauna, where 

 it is represented by S. mucronatus, S. segrnentus. Hall, S. bimesialis. Hall, S. subat- 

 tenuatus. Hall, S. varicosus, Conrad. 



III. FiMBRiATi. Typical examples, Spirifer fimbriatus, Conrad, S. lineatus, 

 Martin, S. arrectus, Hall. 



(la) 1842. Orthls, Vanoxem. Geology of N. Y. ; Rej>t. Third Dist., ]i. 112, figr. 1. 

 (16) 1842. 0)77hs, Vanuxem. Geolog-y of N. Y. ; Kept. Third Dist., i>p. 91, 94. 



