868 DR F. R. C. REED ON THE 



marked with 7-9 strong equidistant straight primary filiform radii, of which one is 

 median and rather stronger than the rest ; a few shorter secondary radii occasionally 

 present ; very delicate concentric lines over whole surface. 



Dimensions. — Length, 6-12 mm. ; width, 10-20 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Remarks. — This shell is very doubtfully referred to the same genus as R, (PI.) 

 deltoidea. The muscle-scar in the pedicle-valve is similar, but the coarse internal 

 pustulation and characters of the brachial valve are more like some species of 

 PI ectambonites or Chonetes. The absence of distinct geniculation is unlike R. (PI.) 

 deltoidea and typical Leptzena, but resembles Plectambonites. The special prominence 

 of the median radius recalls Raf. [Leptaena ?] unicostata (Meek and Worthen), # of 

 which the generic position is disputed, but the diductor muscle-scars are much smaller 

 and more compact, though the general shape of the shell is not unlike it. 



Rafinesquina (Playfairia) Ricliardsoni, sp. no v. 

 (Plate XII, figs. 11, 12.) 



Shell small, transverse, strongly geniculated at about half its length, widest at 

 hinge-line ; cardinal angles acutely pointed, produced, subfusiform. Pedicle-valve 

 with flattened disc, slightly elevated towards beak ; geniculation abrupt, rounded ; 

 beak small, pointed ; hinge-area making acute angle with disc. Brachial valve 

 concave ; beak inconspicuous. Surface of valves covered with regular thread-like 

 rounded lines of subequal size, but every third or fourth one is very slightly larger 

 and the median one is stronger and more prominent than any of the rest. Interior 

 unknown. 



Dimensions. — Length, 9'0 mm. ; width, 14'5 mm. 



Horizon. — Whitehouse Group. 



Locality. — Shalloch Mill. 



Remarks. — The external distinction between this species and R. deltoidea consi3ts 

 in the ornamentation ; the single strong median primary radius and the almost 

 equal strength of the other radii, without any conspicuous differentiation into two 

 series, at once strike the eye. In respect of the median radius we may compare 

 R. declivis, James, f and R. mediocostalis, Reed,* but it cannot be considered identical 

 with either. This species is named after the Rev. Peter Richardson of Dailly, who 

 collected many of the Girvan trilobites figured by Nicholson and Etheridge. 



* Meek and Worthen, Geol. Surv. Illinois, iii (1868), p. 335, pi. 4, fig. 11 ; Hall and Clarke, op.cit., Brach., i, 

 pi. xva, fig. 39, pi. xx, fig. 25 ; Winchell and Schuchert, Geol. Surv. Minnesota, Palseont., iii (1893), ]>. 411, pi. 

 xxxii, figs. 6-9. 



t Fokrste, Bull. Venison Univ., vol. xvi, art. 2, p. 43, pi. ii, fig. 4 ; pi. v, figs. 12a-d. 



I Reed, Geol. Mag., dec. v, vol. ii (1905), p. 449, pi. xxiii, figs. 10, 11. 



