BRACHIOPODA. 439 



Dalmunclia.] 



number of plications, with a convex ventral valve. In 0. pectinella this valve is 

 flatter and its cardinal area is never so strongly elevated as in 0. ichitfieldi. 



Formation and locality Common in the Hudson River group at Spring Valley and near Granger, 

 Minnesota; Delaflcld, Wisconsin; Savannah, Illinois, and Graf, Iowa. 



Collectors. E. O. Ulrich. John Kleckler, W. H. Scofleld and the writers. 

 Mus. Reg. Nos. 277, 429, 4094, 5549, 7762-7764. 



Subgenus DALMANELLA Hall. 



1892. Dalmanella. HALL. Palaeontology of New York, vol. viii, pt. i, p. 205. 



Original description: "Shells plano-convex or subequally biconvex. Pedicle 

 valve usually the deeper, often gibbous, elevated at the umbo and arched over the 

 cardinal area. Hinge-line generally shorter than the greatest width of the shell. 

 In many of the species there is a more or less conspicuous, undefined median fold 

 and sinus on the pedicle and brachial valves respectively. Surface covered with 

 fine, rounded, bifurcating striae. 



" In the pedicle valve the teeth are quite prominent, thickened at their extremi- 

 ties and supported by lamellae which are produced forward circumscribing a rather 

 short suboval or subquadrate muscular area, which is more or less distinctly defined 

 in different species and in different conditions of the shell. In Orthis meeki Miller, a 

 somewhat ponderous, biconvex, multistriate variation of Orthis testudinaria, it is 

 clearly resolvable into adjuster and diductor scars, the latter bounding, but not alto- 

 gether enclosing the impression of the adductors; the pedicle scar is also discernable. 

 In the brachial valve the cardinal process extends forward as a ridge to the bases of 

 the crural plates, where it is broadened and continued thence as a median ridge 

 separating the muscular impressions. The inner surface of this process is divided 

 by a faint median furrow which produces two lobes at the posterior extremity, and 

 each of these lobes is again divided, making the process quadrilobate. Sometimes 

 the inner divisions of the two main lobes have coalesced, producing a strong median 

 lobe and thus making the process appear trilobate. In some species at maturity, and 

 in others from abnormal growth, this process -becomes a broad plug, which fills the 

 entire delthyrial opening. The dental sockets are small, the crural plates often 

 greatly elevated, especially in the plano-convex forms, and they are not usually 

 produced into a ridge about the muscular area, but end abruptly. Muscular 

 impressions quadruplicate, sometimes with radiating ridges extending from the 

 lateral and anterior margins. 



" Shell substance finely fibrous and punctate." 



Species of this subgenus probably make their appearance as early as the Calcif- 

 erous (0. electra Billings), but certainly in the Chazy group, and are also known to 

 occur in all the intervening formations up to the close of the Devonian. 



