808 DR F. R. C. REED ON THE 



Genus Lingulasma, Ulrich. 



Lingulasma ? ardmillanense, sp. no v. 



(Plate II, figs. 20-23.) 



Shell biconvex, elongated oval, about twice as long as wide ; sides subparallel, 

 nearly straight ; anterior end rather abruptly rounded, sub truncate. Pedicle-valve 

 gently convex ; beak acuminate, with shoulders meeting at about 75° ; interior 

 with large low triangular platform slightly pointed in middle, extending nearly 

 across width of valve and for more than one-third its length. Brachial valve 

 with blunter beak ; surface gently convex ; interior with long straight median 

 septum starting a little in front of beak and reaching about three-fourths the length 

 of valve, dividing platform ; platform low, more than half length of valve, with 

 median tongue projecting anteriorly, arched forwards and bearing at base of 

 tongue a pair of nearly contiguous oval " central " muscle-scars. Surface of shell 

 ornamented with closely placed, somewhat irregular, minutely sinuous thin imbri- 

 cated concentric lamellae. 



Dimensions. — Length, 18"0 mm. ; width, 9 "5 mm. 

 Horizon. — Balclatchie Group. 

 Locality. — Ardmillan. 



Remarks. — -The shape of the shell is much like that of L. nympha, Billings,* of 

 the Quebec Group, and L. philomela, Billings,! of the Trenton Limestone. It is also 

 similar to that of L. longissima, Pander, as interpreted by M'Coy and Davidson.} 

 But the internal characters are those of Lingulasma as described by Ulrich § and by 

 Hall and Clarke,|| though the platform is less elevated and solid. 



Lingulasma ? canadense (Billings). 



(Plate II, fig. 24.) 



1862. Lingula canadensis, Billings, Geol. Surv. of Canada: Palseont., vol. i, p. 114, fig. 95. 

 1877. Lingula canadensis, Billings'?, Davidson, Geol. Mag., N.S., vol. iv, p. 16, pi. ii, figs. 4, ia-c. 

 1883. Lingula canadensis, Billings?, Davidson, Mon. Brit. Foss. Brach., vol. v, Silur. Suppl., p. 202 ; 

 pi. xvii, figs. la-c. 



Davidson's figure of the ornamentation of the specimen from Balclatchie, which 

 he attributed to Billings' species Lingula canadensis, is not correct ; the concentric 

 raised rounded lines are not drawn sufficiently thick, and the tubercular swellings 

 resulting from the crossing of the finer equidistant radial and thicker concentric lines 

 are made too large, too circular, and too close together. The tubercles are in reality 

 small, laterally compressed, annular, and rarely contiguous. There is a fragment of a 



* Billings, Palseoz. Foss. Canada, vol. i (1862), p. 214, fig. 198. 



t Billings, op. cit., p. 49, fig. 53. 



\ Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, p. 51, pi. iii, figs. 28-30. 



§ Ulrich, Amer. Geol, iii, 1889, p. 389, fig. 5 on p. 378. 



|| Hall and Clarke, Palseont. New York, vol. viii, 1892, Brach., i, p. 24, pi. ii, figs. 17-23. 



