306 MR. E. S. COBBOLD ON TRILOBITE3 [Aug. I9U» 



Orthis (Ortjsia) cf. lenticttlaris Wahlenberg. (PL XXVI, 

 figs. 24-26.) 



Cf. Orthis (Oriisia) lenticularis Walcott, Proc. U. S. Nat. Mus. No. 1395, 

 vol. xxviii (1905) p. 273, where numerous references to earlier authors will 

 he found quoted. 



This species occurs as casts in the Shoot-Rough-Road Shales, in a 

 micaceous shaly sandstone. Owing to the relative coarseness of the 

 matrix, the surface-characters are poorly preserved, yet sufficiently 

 to indicate that the ribbing of the shell was rather bold and was 

 crossed by strong concentric lines of growth. Both valves are 

 moderately convex, the pedicle-valve slightly more so than the 

 brachial, the former having an obscure fold (?) and the latter a well- 

 marked triangular sinus. 



The majority of the specimens from the lower section on the 

 Shoot-Rough Road, Comley, are quite small, about 2 to 2| milli- 

 metres long by 3 to 3J mm. in width. They are distinctly smaller 

 than the specimens obtained from the Dolgelly Beds of North 

 Wales. Further examples, from a rottenstone band in similar 

 shales in the field north of the same spot, at a horizon perhaps 

 rather higher than that of the lower section, are larger, ranging up 

 to 6| millimetres in width. 



The imperfect preservation of these shells, as also their small size, 

 renders their specific correspondence with the Dolgelly form a 

 matter of uncertainty. Orthis lenticularis is found in North Wales, 

 Sweden, Norway, and North and South America, and is charac- 

 teristic of the Peltura Fauna of the Upper Cambrian. The speci- 

 mens here described may belong to a lower zone. 



Orthis ? sp. (PI. XXVI, figs. 27 a & 27 6.) 



The only specimen found consists of a fragment of a nearly-flat 

 valve, covered with numerous rounded costae separated by narrower 

 rounded interspaces and crossed at intervals by imbricating growth- 

 lines. Though too incomplete for identification, it differs from all 

 other known species of British Cambrian brachiopoda. 



Locality and horizon. — 'The upper section on the Shoot- 

 Rough Road, Comley ; from the main mass of the Shoot-Rough-Road 

 Flags, in the same bed as BillingseUa cobboldi, about 4 feet below 

 the band yielding Paradoscides davidis. 



EXPLANATION OF PLATES XXIII-XXVI. 



Plate XXIII. 



Parad oxides gr oo mil Lapw. (See p. 283.) 



[All the figures are of the natural size.] 



Pig. 1. Pax*t of dome of glabella [A 1 ]. 



2. Part of glabella showing furrows [A 2 ]. 



3. Occipital ring [B 7 ]. 



4. Free cheek [JJJ : a, under side ; b, section at the wide end. 



5. External cast of the tip of one of the anterior pleurae [A 7 ] : a, concave 



view ; b, sectional view. 



