DISCINID^. 723 



Disdna pileolus Salter, Davidson, 1871, British Fossil Brachiopoda, vol. 3, pt. 7, No. 4, p. 344, PL XLIX, figs. 41^2. 



(Original description, Davidson, 1868, pp. 312-313, copied. Figs. 41 and 42 are copied from Davidson, PI. XVI, 



figs. 12 and 11, respectively.) 

 Not Disdna pileolus? Hicks, 1871, Quart. Jour. Geol. Soc. London, vol. 27, pt. 1, PI. XV, figs. 12 and 12a. (Referred 



in this monograph to Stenotheca.) 

 Orbiculoidea pileolus (Salter), Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 137. (Changes 



generic reference.) 



The original description by Davidson [1868, p. 312], follows: 



Shell very small, circular or slightly longitudinal oval, rather broader anteriorly; about two and a half lines in 

 length and a little less in breadth. Dorsal valve conical. Ventral valve slightly convex, depressed near the margin; 

 vertex in both valves at a short distance from the center, as also the foramen (?) in the ventral valve. Surface marked 

 with concentric lines, which are more strongly marked in the ventral valve. Interior not known. 



I have not been able to secure specimens of this interesting shell, so can not add any per- 

 sonal observations upon it. Hall and Clarke [1892c, p. 137] suggest its reference to Orbiculoidea 

 and in this, from our present information, I concur. As they have pointed out, it is the oldest 

 representative of the genus. 



Hicks [1871, PL XV, fig. 12] illustrates a depressed conical shell from the "Red" beds at the 

 base of the "Purple" rocks, about 3,000 feet below the base of the Middle Cambrian "Menevian 

 group" as "Disdna pileolus." Later [1881, p. 297] he calls the species "Disdna casrfaiensis." 

 To me the shell is more suggestive of the gastropod genus Stenotheca than of a brachiopod 

 and until I can obtain better material it will be so referred. 



Formation and locality. — Middle Cambrian: (318e) Lower portion of the Menevian at Camlan, North Wales; 

 (318d) sandstones in the middle portion of the Menevian at Porth-y-rhaw, St. Davids, South Wales; (318p) sandstones 

 in the middle portion of the Menevian at Ninewells, near St. Davids, South Wales; (318q) yellowish-gray beds in the 

 Harlech group, on the road between Solva and Whitechurch, St. Davids, South Wales; and (318r) sandstones in the 

 middle portion of the Menevian at Solva Harbor, St. Davids, South Wales; all [Davidson, 1871, pp. 344 and 345] in 

 Wales. 



Orbiculoidea varians (Barrande). 

 Plate LXXXI, figure 8. 



Disdna variant Barrande, 1868, Faune silurienne des environs de Hof, en Bavifere, pp. 103-104, fig. 71. (De. 



scribed in French as a new species. Fig. 71 is copied in this monograph, PL LXXXI, fig. 8.) 

 Disdna varians Barrande, 1868, Neues Jahrb. fiir Mineralogie for 1868, p. 692, unnumbered plate, fig. 71. (Copy 



of preceding reference.) 

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



The original description by Barrande follows: 



The form of this species is always elongated, but in proportions varying somewhat with the individuals. The 

 surface is slightly arched. The summit is somewhat beyond the center of the figure, which is an ellipse, slightly 

 truncated at the small end near the perforation. The perforation is linear and less than 1 mm. in length. The frag- 

 ments of the shell that remain present traces of fine concentric strise. The imperforate valve has not been observed. 

 Length, 6 mm.; breadth, 5 mm. 



Ohservations. — I am not able to add to the above description. It is evident that the species 

 is not a Disdna, as that genus is now understood, but with only a single figure and the above 

 description it is not practicable to make a satisfactory generic reference. The subcentral apex 

 with the elongate slit back of it, is more suggestive of Orhiculoidea than any other genus of the 

 lower Paleozoic fauna. 



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

 1868a, p. 103]) 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. 



