ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 857 



finer ones seem intercalated near the margin. The whole shell is closely and 

 minutely punctate. A comparison of these specimens with examples of Lindstrom's 

 0. visbyensis* from Gotland, shows that a very close similarity exists between them. 



Dimensions. — Length, 13-19 mm. 



Horizons. — (l) Saugh Hill Group ; (2) Penkill Group. 



Localities. — (l) Woodland Point; (2) Penwhapple Glen. 



Subgenus rhipidomella, Oehlert. 

 Orthis (Rhipidomella) polygramma, Sowerby, var. pentlandica, Davidson. 



1868. Orthis pohjrjrumma, var. pentlandica, Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, p. 219, 

 pi. xxix, figs. 4-10. 



1883. Orthis polygramma, var. pentlandica, ibid., vol. v, Silur. Suppl., p. 179, pi. xiii, figs. 15, 16. 

 1 1883. Orthis reversa, Davidson, ibid., vol. v, Silur. Suppl., p. 180, pi. xvi, fig. 13; and p. 225. 

 ? 1868. Orthis turgida, Davidson (pars), ibid., vol. iii, pi. xxxii, fig. 18 (non cet.). 



This variety of O. polygramma was sufficiently described by Davidson, but his 

 figures are restorations of the actual specimens from Girvan. No interiors are known 

 from Girvan, and those figured by Davidson belong to examples from the Pentland 

 Hills. It may be mentioned that the thread-like ribs are rounded, not acute, and 

 that there are minute pits between them as in Orthis' 1 . punctostriata, Hall.t It is 

 probable that the specimen from Woodland Point figured as O. reversa belongs to 

 this species. 



Horizons. — (l) Penkill Group ; (2) Saugh Hill Group ? 



Localities. — Penwhapple Glen and Burn, Penkill ; (2) Woodland Point. 



Orthis {Rhipidomella) prematura, sp. no v. 

 (Plate X, figs. 17, 18.) 



Shell suboval, somewhat subquadrate, widest near front, longer than broad ; 

 hinge-line less than maximum width of shell ; cardinal angles obtuse. Pedicle-valve 

 gently convex, with small slightly elevated incurved beak ; interior of pedicle-valve 

 with large oval muscular scar two-thirds the length of valve, with sharp raised lateral 

 margins but undefined in front, composed of two large elongate flabelliform diductors 

 separated by a narrow median ridge becoming stronger and stouter in the middle of 

 the valve but dying out a little in front of muscle-scar ; ovarian areas marked with 

 a few large pits, more or less elongated, and fused radially. Surface of valve 

 covered with very numerous (170-200) regular equal closely placed fine rounded 

 riblets curving back slightly on each side near hinge-line. 



Dimensions. — Length, 20 mm. ; width (maximum), 17 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



* Lindstrom, Ofvers. k. vet. Akad. Forhandl., No. 8, 1860, p. 366, pi. xii, fig. 8. 



t Hall, Palmont. New York, ii, 1852, p. 254, pi. Iii, figs. 5a-/; Grabau, Bull. N. Y. State Mas., No. 45, vol. ix, 

 1901, p. 186, fig. 95. 



