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- 

 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, 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 pedick-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 Pentamerm galeatus, Dalman, have a very considerable 



"^ Petiefactenkuinie Deutschlanda ; Biachiopoden, 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 Antikhtnchonella, it is the ConchicUum teimistriatus, Walmstedt, mentioned in imme- 

 diate connection with the sinijle use of this name, and noi{Pentamerus linguifer, which is cited by Quexstedt 

 as an illustration of the fact that the position of fold and sinus in the pentamei-oids is sometimes the same 

 as in the Rhynchonellas. Antikhynchonella if adopted would be simply synonymous with CoxCHiDinM. 



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

 latter is quite variable, the typical form from the grits and limestones having' rather broad ami shallow 

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

 larger, sometimes very arcuate and tinely i-ibbed. 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 desci-ip- 

 tion of this shell the name has come into use as P. 'papillcmensi.t. We take this opportunity of coi'i-ecting it 

 to Pavilionen.'iis, the current form being meaningless. 



