60 Prof. T. E. Jones and Dr. H. B. Holl on 



13. Beyrichia Wilckensiana^ Jones, op. cit. p. 89. Horderley, 



Shropshire. 



14. Gythere Aldensisj M^Coy, sp. Aldeans, Ayrshire. Re- 



specting this last species it is advisable to give here all 

 the particulars we know of it. 



Gythere Aldensis, M'Coy, sp. PI. VII. fig. 12. 



Ct/theropsis, n. sp. M'Coy, 1851. Rep. Brit. Assoc, for 1850, Trans. Sect. 



p. 107. 

 Q/theropsis Aldensis, M'Coy, 1851. Ann. N. Hist. ser. 2. vol. viii. p. 387. 

 Cythe^'opsis Aldends, M'Coy, 1852. Syst. Descr. Pal. Foss. Geol. Mus. 



Cambridge, pi. 1 L. fig. 2. 

 Cytheropsis Aldensis (M'Coy), Salter, 1859. In Murchison's ' Siluria,' 



2nd edit. p. 539. 

 Cythere ? Aldensis (M'Coy, sp.), Jones, 1867. In Murchison's ^ Siluria/ 



3rd edit. p. 517. 



In his memoir " On some New Cambro- Silurian Fossils/' 

 1851 (Ann. Nat. Hist. I. c), Prof. M'Coy thus describes this 

 species : — 



" Arcuato-oblong, dorsal margin much arched, greatest convexity 

 about the middle, sloping more towards the anterior, which is 

 slightly smaller than the posterior end ; posterior end broadly arched, 

 anterior end obtusely pointed ; a concave flattened sinus, rather 

 more than half the length of the shell, in the ventral margin, rather 

 nearer to the anterior than the posterior end ; an obscure roughened 

 spot slightly nearer to the anterior than the posterior end, and 

 slightly nearer to the dorsal than the ventral margin; valves 

 moderately and evenly gibbous ; surface very minutely punctured, 

 under a strong lens. Length 1^ millimetre, depth about two-thirds 

 the length. 



*' This little species is accompanied by a more elongate, oblong, 

 less arched form, of greater rarity, which may either be a distinct 

 species or the male. 



*' Extremely abundant in the dark earthy Hmestone of Aldens, 

 Ayrshire." 



In the Woodwardian Museum at Cambridge are preserved 

 some specimens of the '^ Lower Bala " Limestone of Aldeans, 

 collected by Prof. Sedgwick in 1850, and containing several 

 (six or seven) small Bivalved Entomostraca, one of which 

 Prof. M^Coy described as above, and figured in the Brit. Pal. 

 Foss. Camb. Mus. part 2. fasc. 1. pi. 1 L. fig. 2. Through the 

 courtesy of Mr. Harry Seeley, one of us has carefully examined 

 these specimens. They are all imbedded to a greater or less 

 extent in the matrix ; and there are at least two distinct forms. 

 One of these we refer to P. Maccoyii (see above, p. 6Q) ; and 

 the most striking of the others is the specimen figured by 

 Prof. M'Coy. What appears as an obscure tubercle, however, 



