BRAOHIOPODA. 755 
2. Aseptati. Those without a median septum in the pedicle- 
valve. These species aremore abundantly plicated, often much 
more extended on the hinge than in the septate group. The 
lamelle are without radial striations. The Aseptati group them- 
selves 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 submucronatus, Hall, in which 
the fold and sinus are not plicate. 
Section ITI. Furerrati. (Plate 25, figs. 1-15.) Typical examples, 
Spirifer jimbriatus, Conrad, S. lineatus, Martin, S. arrectus, Hall. 
Shells with few low plications or none ; hinge-line not greatly 
extended, often shorter than the greatest diameter of the shell; 
dental lamelle moderately, sometimes notably developed; a low 
median septum may exist in the pedicle-valve. Surface covered 
with concentric rows of fringes or fine spines. 
This group is divided into: 
1. Unicispinei = Dettayris, Dalman, 1828, sensu stricto; 
those species in which the concentric fimbrie are made up of 
short, simple, hollow spines. These are the early fimbriate 
species, the type of structure not extending, so far as now known, 
beyond the Devonian. The shells are distinguished from the 
other fimbriate Spirifers by their more extended and more dis- 
tinctly plicated surface and the prominent, often sharply devel- 
oped fold and sinus. Their more characteristic representatives 
in the American Palexozoic are Spirifer crispus, Hisinger, and 
var. simplex, Hall, of the Niagara faunas; S. Vanwwemz, Hall, of 
the Tentaculite limestone, S. Saffordi, S. octocostatus, Hall, of the 
Lower Helderberg group, S. arrectus, 8. tribulis, Hall, of the 
Oriskany sandstone and S. dwodenarius, Hall, of the Corniferous 
limestone. This is the (a) S. evtspus-type. 
An interesting series of forms which has had’a parallel develop- 
ment with the S. crispus-type begins with the S. bicostatus, 
Vanuxem, and var. petilus, Hall, in the Niagara group, is repre, 
sented by S. modestus, Hall, in the Lower Helderberg group, S. 
Canandaigue, from the Hamilton group, and possibly, 8. wrbanus- 
Calvin, from a corresponding horizon in Iowa, the line terminat- 
ing in (b) S. devis, Hall, from the lower Portage shales, 
7 
