Mr. R. Etherklge on Carboniferous Lamellibranchiata. 97 



striae do not reacli the umbone.s. All specimens of the left 

 valve which have come under my notice show faint indications 

 of concentric lines of j^rowth, which probably slightly pecti- 

 nated the radiating ribs. 



In general form this species is also allied to A. Icnockon- 

 niensi'sj M'(Joy* ; however, one valve of that shell is said to 

 have only twelve large rounded ribs, with a fine sharp ridge 

 on each side, each set of three ribs being separated from the 

 next set by a narrow space. This is quite different from 

 the ornamentation of cither valve of A. subconoithats. 



Loc. ami Horizon. Dark sandstone of Knockhill Quarry, 

 Strathkiiniess, near St. Andrews ; cement-stone group of the 

 Lower Carboniferous series. Cabinet of Dr. Traquair and 

 coll. Geol. Survey of Scotland. 



Aviculoijecien ccelatuSj M'Coy? 



Pecten Cfplatus, M'Coy, Synopsis Carb. Foss. Ireland, 1844, p. 90, t. 18. 

 f. 2; Tennant, Strat. List Brit. Foss. 1847, p. 101 (without descrip- 

 tion) ; D'Orb. Prodrome de Pal. 1840, i. p. l-iO (-n-ithout description). 



Avicuiopedni ccflattis, M'Coy, Brit. Pal. Foss. p. 483, t. 3 E. f . 5 ; 

 Morris, Cat. Brit. Foss. 18-34, 2nd ed. p. 1(54 (without description); 

 Huxley & Etheridge, Cat. Foss. Mus. Pract. Geol. 1805, p. 110 (with- 

 out descriptiou). 



>Sp. char. Shell ovate to deltoid, slightly convex, most so 

 at one third from the beaks, gradually flattening to the mar- 

 gins; height about equal to the length. Anterior ear of the 

 right valve elongate, well divided from the body of the shell, 

 ornamented by coarse ridges parallel to the margin, and cros.sed 

 by three to five radiating ridges ; anterior ear of the left valve 

 less divided from the body of the shell, smaller, with concen- 

 tric imbricating flattened lamina?. Posterior ears pointed, with 

 numerous radiating ridges and concentric frilled imbrications. 

 Hinge-line not so long as the shell, with numerous tooth-like 

 spines extending to the extremities of the ears ; those on the 

 anterior ears more curved than the others. Left valve orna- 

 mented by a large number (^I'Coy says sixty) of simple, sub- 

 equal, rounded, radiating costte, cro.^sed by close, concentric 

 rows of regularly frilled or arched imbrications. The surface 

 of the right valve also with radiating costa?, but the concentric 

 imbrications much flatter, giving to it a roughly reticulate ap- 

 pearance ; margins crenulate (?). 



Obs. The above description has been drawn up from a series 

 of specimens which, altnough differing slightly in some of 

 their minor characters from the typical specimen, nev^erthelcss 



* Synopsi.o, p. Oo. t. 17. f. 4. 



