60 Prof. T. R. Jones and Dr. H. B. Holl on 
13. Beyrichia Wilckensiana, Jones, op. cit. p. 89. Horderley, 
Shropshire. 
14. Cythere Aldensis, M‘Coy, sp. Aldeans, Ayrshire. Re- 
specting this last species it is advisable to give here all 
the particulars we know of it. 
Cythere Aldensis, M‘Coy, sp. Pl. VII. fig. 12. 
Cytheropsis, n. sp. M‘Coy, 1851. Rep. Brit. Assoc. for 1850, Trans. Sect. 
nLOTe 
Cytheropsis Aldensis, M‘Coy, 1851. Ann. N. Hist. ser. 2. vol. viii. p. 387. 
Cytheropsis Aldensis, M‘Coy, 1852. Syst. Descr. Pal. Foss. Geol. Mus. 
Cambridge, pl. 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. 7. 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 14 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 limestone 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. pl. 1 L. fig. 2. Through the 
courtesy of Mr. Harry Seeley, one of us has carefully examined 
these specimens. ‘l'hey 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. 56) ; and 
the most striking of the others is the specimen figured by 
Prof. M‘Coy. What appears as an obscure tubercle, however, 
