BRACHIOPODA. 
17 
Mr. Davidson has referred two Devonian species to Spirif'ertna, S. cristata 
Schlotheim, var. octoplicata, and S. insculpta, Phillips (?), both of which are 
described as having a punctate structure. It is not known, however, whether 
in these early forms the loop has attained its ultimate development; we might 
expect to find it with its lateral branches discrete as in the true Spirifers. 
The species of this septate section have, so far 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 8 . Kentuckiensis and S. solidirostris, 
which resemble very closely in other respects these septate lamellose Spirifers, 
are fimbriated. 
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, multiplicate shell with a single low plication in 
the sinus and a corresponding depression on the median fold; the other, (b), 
Spirifer submucromtus, 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. Cumberlandm, 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. segmentus, Hall, S. bimesialis, Hall, S. subat- 
tenuatus, Hall, S. varicosus, Conrad. 
HI. Fimbriati. Typical examples, Spirifer fimbriatus, Conrad, S. lineatus, 
Martin, S. arrectus, Hall. 
(la) 1842. Orthis, Vandxem. Geolog-y of N. Y. ; Rej)t. Third Dist., p. 112, fig-. 1. 
(lb) 1842. Orthis, Vanuxem. Geology of N. Y. ; Kept. Third Dist., pp. 91, 94. 
