722 CAMBRIAN BRACHIOPODA. 



Superfamily DISCINACEA Waagen. 



FamUy DISCINID^ Gray. 



Genus ORBICULOIDEA d'Orbigny. 



For synonymy, description, and discussion of this genus the student is referred to the 

 memoir of Hall and Clarke [1892c, pp. 120-137]. The genus has been recently classified [Wal- 

 cott, 1908e, PI. XI, and pp. 142 and 147]. 



Two Upper Cambrian species are tentatively referred to the genus: 0. varians (Barrande) 

 and 0. contraria (Barrande), and one Middle Cambrian species, 0. pileolus (Salter). 



Orbiculoidea contraria (Barrande). 

 Plate LXXXI, figure 9. 



Discina contraria Barrande, 1868, Faune silurienne des environs de Hof, en Bavifere, p. 104, fig. 72. (Described 



in French, as a new species; see below for translation. Fig. 72 is copied in this monograph, PL LXXXI, fig. 9.) 

 Genre? sp. nebulosa Barrande, 1868, idem, pp. 105-106, fig. 69. (Described and discussed in French as a new 



species.) 

 Discina contraria Barrande, 1868, Neues Jahrb. fiir Mineralogie for 1868, pp. 692-693, xmnumbered plate, fig. 72. 



(Copied from Barrande, 1868a; p. 104, fig. 72.) 

 Genre? sp. nebulosa Barrande, 1868, idem, pp. 693-694, unnumbered plate, fig. 69. (Copied from Barrande, 1868a, 



pp. 105-106, fig. 69.) 

 Discina contraria Barrande, Pompeckj, 1896, Tremadoc Fossilien bei Hof, p. 4. (Occurrence mentioned in German.) 



The original description by Barrande foUows: 



This form, decidedly transverse, contrasts with the preceding, which is elongated. It also forms an ellipse, which, 

 however, is truncated on the larger side. The shell presents only a slight bulge. The summit is placed somewhat 

 beyond the center, going toward the truncated edge. Starting from the summit, the surface forms an inclined plane 

 up to the contour. The perforation is linear and very short. The shell, partly preserved, presents very marked con- 

 centric striae, at unequal intervals. 



Longitudinal diameter, 6 mm.; transverse diameter, 9 mm. 



Observations. — Pompeckj [1896a, p. 4] states that this species was found much more 

 frequently than 0. varians (Barrande), and that rather convex shells, 10 mm. long and 12 mm. 

 broad, were not rare. 



The generic relation of this species is doubtful. It is not Discina, nor from the evidence 

 available can it be referred without question to Orbiculoidea. 



Pompeckj, in reply to my inquiry as to whether he had identified "Genre? nebulosa" of 

 Barrande, wrote as foUows imder date of August 7, 1906: 



As to the nebulosa by Barrande (Faune silurienne des Environs de Hof, fig. 69) I find in notes made on the Barrande 

 originals (in the collection of the Oberbergamt-Munich) that "nebulosa" is to be identified with Barrande's Disdna 

 contraria, 1. c, figure 72. Both are pedicle valves of Discina with the characteristic perforation of that family below 

 the apex. Both figures are incorrectly given. The two sharp lines radiating from the apex in figure 69 are only caused 

 by pressure of the somewhat high shell, and in figure 72 the concentric strise are indeed much more delicate than in 

 the figures which represent an interior cast only, with bits of the shell in the upper part, i.e., near the hinge line. 



Exact determination of these shells is very difficult; most of them (I saw more than a hundred) are compressed, 

 crumpled, deformed, very seldom the apical region is clearly to be seen; shell rarely preserved; but there is indeed no 

 doubt that they must belong to the Discinidse on account of the "Schlitz" below the apex. There is no sharp differ- 

 ence between the rounded form, named Discina varians by Barrande, and between the larger and wider form, D. 

 contraria, or nebulosa. 



Formation and locality, — Passage beds between the Upper Cambrian and the Ordovician: (303c [Barrande, 

 lS68a, p. 104]) suburbs of Hof ; and (303f [Pompeckj, 1896a, pp. 7 and 8]) railway cut near Schellenberg, a little distance 

 back of the railway station at Neuhof, near Hof; both in Bavaria, Germany. 



Orbiculoidea pileolus (Hicks MS.) (Salter). 

 Plate LXXXI, figures 11, 11a. 



Discina pileolus (Hicks MS.) Salter, 1866, Kept. British Assoc. Adv. Sci. for 1865, p. 285. (Mentioned.) 

 Discina pileolus Salter, Davidson, 1868, Geol. Mag., vol. 5, pp. 312-313, PL XVI, figs. 11-12. (Described and dis- 

 cussed; see p. 723 for copy of description. Figs. 11a and 12a are copied in this monograph, PL LXXXI, 

 figs. 11 and 11a, respectively.) 



