850 DR F. R. C. REED ON THE 



shape, size, and other characters. Some Mulloch . Hill specimens show the internal 

 characters in internal casts. 



Horizons. — (l) Penkill Group ; (2) Camregan Group ; (3) Mulloch Hill Group. 



Localities. — (l) Penkill ; (2) Bargany Pond Burn ; (3) Mulloch Hill, Craigens. 



Orthis (Dalmanella) elegantula, Dalman. 



182S. Orthis elegantula, Dalman, Vet. Akad. Handl., p. 117, pi. ii, fig. 6. 



188o. Orthis elegantula, Dalman, Davidson (pars), Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., 

 pp. 178, 226. 



The typical form of 0. elegantula occurs at Woodland Point, Mulloch Hill, 

 Penkill, and Newlands. The ribbing in poorly preserved specimens and indeed at 

 all times is difficult to distinguish from 0. crassa, but the shape of the valves and 

 prominence of the beak of the pedicle-valve generally permit of the separation of the 

 species. I have refrained above from quoting the usual long synonymy and list of 

 references given by Davidson and others for this species, for undoubtedly there are 

 many erroneous identifications, and a re-examination of the material is most desirable. 



Horizons. — {!) Saugh Hill Group ; (2) Mulloch Hill Group ; (3) Penkill Group. 



Localities. — (l) Woodland Point, Newlands ; (2) Mulloch Hill, Craigens ; (3) 

 Penkill. 



Orthis {Dalmanella) elegantula, Dalman, var. nov. drummuchensis. 



(Plate IX, figs. 11-15.) 



1883. Orthis elegantula, Dalman, Davidson (pars), Mon. Brit, Foss. Brack., vol. v, Silur. Suppl., 

 pp. 178, 226. 



The small shells labelled by Davidson as 0. elegantula from the Starfish Bed 

 appear to belong to a more or less distinct variety as regards the ribbing, and are 

 certainly separable from the Silurian shells passing under that name. In shape they 

 have the usual typical oval or subcircular form and the usual relative convexity of 

 the two valves. The ribs, however, curve back on each side, are subangular, rather 

 unequal in size, increasing by unequal bifurcation at about one-third their length 

 and again at about two-thirds their length ; on the margin they are usually of 

 subequal size, and number about 60 in an average shell of 8-9 mm. long. The fine con- 

 centric lineation is strongly marked. The interior of the pedicle-valve shows the usual 

 oval muscle-scar, strongly margined laterally by sharp edges, but rather indefinite 

 behind. Comparison with typical examples of 0. elegantula from Gotland, named by 

 Lindstrom, shows that in the latter the ribs are more regular, less angular, and do not 

 have the second division. This variety appears to be closely related to Dalmanella 

 jugosa, James,* of the Ohio Ordovician. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



* Foerste, Bull. Denison Univ., vol. xiv (1909), p. 218, pi. iv. figs. 16, a, b ; id., Ohio Naturalist, 1912, 

 pi. xxii, figs. 1a-g. 





