BRACHIOPODA. 
245 
fold and sinus the reverse of that in Rhynchonella.* It is therefore proposed 
to designate them by the term Barrandella. 
The term Pentamerella, Hall (1867), embraces, in a broad sense, the Devo- a -.. r 
nian representatives of the same type of exterior, though the latter present 
some structural differences. The shells are of larger size than those of 
Barrandella and strongly plicate, possessing a very narrow cardinal area, an 
elongate pseudo-area, and incipient deltidial plates. The median septum on the 
interior of the pedicle-valve is very short, and at times is altogether absent. 
In the brachial valve the crural plates and supporting septa form a distinct 
spondylium which is broadly sessile on the surface of the valve. The typical 
form of this division is the Atrypa arata, Conrad, a shell which abounds in the 
Schoharie grit and Corniferous limestone, and with it have been associated 
these other Devonian species; P. Pavilionensis, of the Hamilton group, 
P. dubia, Hall, P. micula and P. obsolescens, Hall, from the middle Devonian 
faunas of Iowa. All of these shells have the ovarian surface of the pedicle- 
valve strongly pitted. 
(B). Galeafiform pentameroids having the fold on the pedicle-valve and the sinus on 
the brachial valve. 
Here we meet with a nearly parallel development to that observed among 3 i'er r.r./L/ 
the Barrandellas and Pentamerellas. In external character there is a greater 
uniformity as the shells are almost invariably plicated and the typical contour 
is subjected to but very slight variation. The Silurian shells which pass 
under the name of Pentamerus galeatus, Dalman, have a very considerable 
^ Petrefactenkunde Deutschlands ; Brachiopoden, p. 231. The term as here employed is simply, the 
“ Antirhynchonella=,” but in the index (p. 727) the Latin form of the name is used. If any species can be 
taken as typical of Antirhynchonella, it is the ConcTiidmm tenui.’ftriatus, Walmstedt, mentioned in imme¬ 
diate connection with the single use of this name, and notlPenfamerus linguifer, which is cited by Quenstbdt 
as an illustration of the fact that the position of fold and sinus in the pentameroids is sometimes the same 
as in the Rhynchonellas. Antibhynchonella if adopted would be simply synonymous with Conchididm. 
t It is often difficult to make a satisfactory distinction between the Hamilton shell and P. arata. The 
latter is quite variable, the tyjncal form from the grits and limestones having rather broad and shallow 
valves and comparatively few, strongly dichotomous ribs. Specimens from the grits are frequently much 
larger, sometimes very arcuate and tinely ribbed. The form prevailing in the Hamilton shales has fewer 
and more simple ribs and is rarely so large as P. arata. By a typogi'aphical ej'ror in the original descrip¬ 
tion of this shell the name has come into use as P. 'papilionenshi. We take this opportunity of correcting it 
to Pamlionen.'iis, the current form being meaningless. 
