916 DR F. R. C. REED ON THE 



of Chonetes proper, and the muscle-scars of the pedicle-valve are more like those of 

 Plectambonites. It seems probable that at least a subgenus should be set up for its 

 reception, and the name Eochonetes may be suggested. According to Twenhofel,* 

 the earliest known appearance of the genus Chonetes is in zone 3 of the Charleton 

 Formation, Richmondian Series (=Upper Ordovician) of Anticosti Island,! but 

 the species there represented is referred to the subgenus Eodevonaria, Breger. 

 Professor 0. T. Jones has attached a MS. name to some examples of this species in 

 Mrs Gray's collection, but his description has not been published. 



Genus Clitambonites, Pander. 



Clitambonites [Orthisina'] ascendens (Pander). 

 (Plate XXI, figs. 12-18.) 



1830. Clitambonites (Pronites) ascendens, etc., Pander, Beitr. Geog. Russ. Reich., p. 72, pi. xvii, 



figs. 2-6. 

 1870. Orthisina ascendens, Pander, Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, p. 278, pi. xlix, 



figs. 27-29. 

 1883. Skenidium Grayiae, Davidson, ibid., vol. v, Silur. Suppl., p. 175, pi. xi, figs. 3, 4, 5. 

 1883. Orthisina ascendens, Pander, Davidson, ibid., p. 175, pi. xvi, figs. 16-18. 



It is curious that while Davidson described and figured Orthisina ascendens 

 from Welsh localities,]; he did not recognise it in the Girvan area, where it is abundant 

 on one horizon, but he described some imperfect specimens of it as a distinct species 

 which he referred to the genus Scenidium as Sc. Grayite. These specimens, and 

 the numerous other better ones from the Starfish Bed which are now available, show 

 all the typical external and internal characters of the genus Clitambonites § and of the 

 species CI. ascendens as interpreted by Davidson. The average length is 20 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Clitambonites complectens (Wiman), var. nov. albida. 

 (Plate XXI, figs. 19, 20.) 



Pedicle-valve very deep, conical, sharply pointed at apex, with rather broad 

 rounded median sinus on surface widening to anterior margin ; cardinal angles 

 acute ; beak small, pointed, not incurved, forming apex of cone. Hinge-area very 

 large, triangular, nearly at right angles to plane of valve, with wide triangular 

 delthyrium nearly one-third the width of valve, having its lower portion covered by 

 convex pseudodeltidium, leaving large oval foramen in upper half; edges of foramen 

 elevated to form basal tube for stalk. Surface of valve covered with regular strong 



* Twknhofel, Canadian Geol. Surv. Museum, Bull. No. 3, 1914, p. 26. 



t Schdchbrt and Twenhofel, Bull. Geol. Soc. America, vol. xxi, 1910, p. 697. 



I Davidson, op. cit., iii, p. 278, pi. xlix, figs. 27-29 ; ibid., Suppl., p. 175, pi. xvi, figs. 16-18. 



§ Halt- and Clarke, Brach., i, p. 233, pi. vii, figs. 23, 24. 



