202 CARBONIFEROUS LAMELLIBRANCHIATA. 



Dimensions. — Fig. 25, PI. XV, Antero-posteriorly. Dorso-ventrally. Elevation of valve. 



measures — . 16 mm. 9 mm. 5 mm. 



The type, fig. 23, PL XV . 12 mm. 7 mm. — 



Localities. — England : Shales below the Millstone Grits, Pule Hill, Marsden. 

 Scotland : Upper Limestone series ; Horizon of the Robroyston or Gare Limestone 

 in rock under George Square, Glasgow. Cement-stone group of the Calciferous 

 Sandstone series ; Brown Sandstone of Knockhill Quarry, Strathkiness, near 

 St. Andrews. Ireland : Arenaceous Shale, Dromard, Draperstown, co. London- 

 derry. 



Observations. — I have little or no hesitation in referring Leda Traquairi, 

 R. Etheridge, jun., to M'Coy's Nucula stilla, although the type specimen of the 

 latter species is very poor. M'Coy's description is as follows : — " Transversely 

 clavate, gibbose, beak nearly central ; posterior [anterior'] side obtusely rounded. 

 Anterior [posterior'] side suddenly contracted, forming a short mucronate beak, 

 rounded at the extremity ; surface very finely striated concentrically." 



It is curious that while Mr. R. Etheridge, jun., contrasted his shell with 

 some American forms, and with Leda attenuata, Fleming, and claviformis, 

 Sowerby, he seems to have ignored the large number of species described and 

 figured by M'Coy (op. cit.). I am not myself at all sure of the specific value of 

 this species, and think it very probable that the collection of a larger number of 

 specimens might demonstrate that it is only a variety of Nuculana attenuata. 

 The surface markings are identical in both forms ; and while the anterior portions 

 of the shells of both are similar, they only differ in the length of the attenuated 

 posterior extremity. 



My opinion seems to be somewhat borne out by observations by Mr. Baily on 

 a series of N. attenuata from Ballyduff, river Bunnow, King's Co., Geological 

 Survey, Ireland, Expl. Sheet 127, p. 9, where he figures two forms of this shell, 

 figs, a and b, the normal shape ; fig. c, " a shorter variety of the same shell : " the 

 latter strongly resembles N. stilla of M'Coy and R. Etheridge, jun. 



Mr. R. Etheridge compared his shell with Nucula Kazanensis, de Verneuil, and 

 Leda bellistriata, Stevens. Mr. Meek considers that the N. Kazanensis of Geinitz, 

 ' Carbon and Dyas in Nebraska,' p. 20, pi. i, figs. 33 and 34, should be referred to the 

 latter species; Nuculana bellistriata, Stevens, is a very small shell, one specimen 

 which I have examined measuring 5 mm. transversely, 3 mm. dorso-ventrally, and 

 2 mm. from side to side, and is altogether different from the species under dis- 

 cussion in shape and comparative dimensions. 



I refigure M'Coy's type specimen of N. stilla, PI. XV, fig. 23. 



The only American species which has any similarity to N. stilla is Nuculana ? 

 curta, Meek and "Worthen, from the St. Louis group of the Lower Carboniferous 

 of Illinois, described in the 'Proceed. Acad. Nat. Sci. Philadelphia' for 1861; 



