ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 813 



of the types and other material. There is no perforation of the beak, as he mentions, 

 but there is a distinct pedicle-groove which is represented as a ridge in his figure 

 (op. cit., pi. xvi, fig. 32) of the interior of a pedicle-valve. This groove is well 

 exhibited in the specimen which he figured as Lingula Ramsayi. The weak median 

 depression in the brachial valve which widens but dies out anteriorly is best seen in 

 the Minuntion specimens. This character is present in Schizambon (Siphonotreta ?) 

 minnesotensis, Hall and Clarke,* from the Trenton Formation, and the characters 

 of the pedicle-valve also closely agree with those of S.Jissus, var. canadensis, Ami.t 

 S. Dodgei, Winchell and Schuchert,| and S. duplicimuratus, Hudson, § are likewise 

 allied species. But Sch. fissus, var. canadensis, was regarded by Hall and Clarke 

 as probably not congeneric with the type species of the genus, Sch. typicalis, 

 Walcott,|| on account of the structure of the pedicle-passage, and it may be necessary 

 to put this whole group of species in a separate genus or subgenus. 



Schizambon scoticus (Davidson) var. 

 (Plate III, figs. 15-17.) 



There is an imperfectly known shell closely resembling Sch. scoticus which occurs 

 in the Starfish Bed, and probably it will have to be regarded as a distinct species when 

 we have better-preserved specimens for study. But at present it may best be placed 

 as a variety of Sch. scoticus. It differs from the Stincliar Limestone form in having 

 (l) a shorter foraminal groove; (2) stronger and more prominent imbricating ridges 

 on the surface ; and (3) fewer and coarser spines. 



Dimensions. — Length, 7-15 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Genus Acrothele, Linnarsson. 



Acrothele medioradiata, sp. nov. 



(Plate III, figs. 18-22.) 



Shell corneous, circular or subcircular. Pedicle-valve low conical, with Ions 

 anterior concave slope and shorter, steeper posterior slope without a definite false 

 area ; apex sharp, prominent, pointed, situated at about one-third the length of the 

 valve, with minute circular foramen at apex and internal narrow groove ending at 

 about three-fourths the distance between apex and posterior margin. Brachial valve 



* Hall and Clarke, Palseont. New York, vol. viii, 1892, Brach., i, p. 177, pi. iv, figs. 37, 38. 

 t Hall and Clarke, ibid., p. 115, pi. iv, figs. 32-36. 



I Winchell and Schuchert, Palseont. Minnes., iii, p. 361, pi. xxx, figs. 5, 6. 

 § Clarke, Rep. State Palseont. 1903, New York State Mus., 1905, Bull. 80, p. 284, pi. 5, figs. 6, 7. 

 || Walcott, Mori. U.S. Geol. Surv., vol viii, 1884, " Pal.tont. Eureka Distr.," p. 69, pi. i, fig. 3 ; id., Camb. Brach. 

 {Mon. U.S. Geol. Surv., vol. li 1912), p. 624, pi. lxxxiv, figs. 1, la-Id. 



