NATURAL HISTORY SOCIETY OF GLASGOW. 267 



line is as wide as the valve, and is bordered by a row of hinge 

 spines, rather strong for the relative size of the shells. The alar 

 expansions are small and the angles rounded. When not distorted 

 the valve acuminates or narrows towards the front, and the form 

 is, speaking in a general way, roughly triangular. The beak is 

 much incurved, overhanging the umbonal region of the shell. 

 There is a small, although well-marked and distinct area (PI. Y., 

 fig. 2), which appears to be longitudinally striated, and perforated 

 by a small foramen or deltidial aperture, elongately triangular in 

 shape. The surface is covered with coarse, strong, radiating ribs, 

 which are simple, as a rule, but occasionally bifurcate, and are 

 separated from one another by valleys about their own thickness 

 in width. The ribs vary from sixteen to eighteen in number. 

 The internal characters cannot be distinguished, except that the 

 radiating ribs are as plainly visible as on the exterior. It is 

 difficult to express an opinion as to the specific identity of these 

 little fossils. The question arises, Is the irregular form an accidental 

 peculiarity, or a specific character 1 If the former, which it pro- 

 bably is, we are dealing with an abnormal variety of Chonetes 

 Buchiana (De Koninck). My friend, Mr. T. Davidson, was kind 

 enough to examine the whole of the specimens, and wrote me as 

 follows :■ — " I have seen young shells of Chonetes Laguessiana, or 

 even G. Buchiana, very like your specimens. When G Laguessiana 

 is very young the ribs are simple, and it is only when the shell 

 gets older that the ribs appear to become more numerous by inter- 

 polation I would have put them down for young 



specimens of C. Laguessiana. It is always very difficult to deter- 

 mine young shells of closely-allied species, for they rarely show 

 the characters of the adult.'"' If these specimens are to be regarded 

 as the young of either of the above species, I think the decision 

 must rest in favour of G. Buchiana, to which they appear to bear a 

 closer resemblance than to G. Laguessiana. 



Locality and Horizon. — Skateraw Quarry, near Dunbar, in shale 

 over the Skateraw limestone ; Kidlaw Quarry, near Gifford, Had- 

 dingtonshire ; East Salton old Quarry, ditto, in shale above the No. 

 2 limestone; Inverteil Quarry, near Kirkcaldy, in shale over the 

 main or No. 1 limestone; Cowdens Quarry, near Dunfermline, a 

 shale over the Linn limestone ; all horizons in the Lower Car- 

 boniferous limestone group (Mr. J. Beanie). 



7. On a small specimen of Or this perforated by a Crinoid stem, 



