BRACHIOPODA. 245 



fold and sinus the reverse of that in Rhynchonella* It is therefore proposed 

 to designate them by the term Barrandella. 



The terra Pentamerella, Hall (1867), embraces, in a broad sense, the Devo- 

 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 

 Bpondylium 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, Hall,f 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). Galeatiform 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 

 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 terra as here employed is simply, the 

 " Antirhynchonfllla-," but in the index (p. 727) the Latin form of the name is used. If any species can be 

 taken as typical of Antirhynchonklla, it is the Conchidium tenui.itriatu.i, Walmstedt, mentioned in imme- 

 diate connection with the single use of this name, and notlPentamenis Unguifer, which is cited by Qdbnstedt 

 as an illustration of the fact that the i)Osition of fold and sinus in the pentameroids is sometimes the same 

 as in the Rhynchonellas. Antirhyncho.vblla if adopted would be simply synonymous with Conchididm. 



t It is often difficult to make a satisfactoi-y distinction between the Hamilton shell and P. arata. The 

 latter is quit* variable, the typical form from the grits and limestones having rather broad and shallow 

 valves and comparatively few, strongly dichotomous libs. Specimens from the grits are frequently much 

 larger, sometimes very arcuate and finely ribbed. The form prevailing in the Hamilton shales has fewer 

 and more simple ribs and is rarely so large as P. arata. By a typographical error in the original descrip- 

 tion of this shell the name has come into use as P. papilumetisii. We take this opportunity of cori-ecting it 

 to Pavilionensis, the current form being meaningless. 



