220 
THE GEOLOGIST. 
somewhat longer tliau the greatest width of the shell, with rectangular or 
sliglitly acute and extended terminations. Both valves are provided with 
narrow sub-parallel areas, the ventral one, which is the largest, being divided 
by a smaU fissure, partially covered with a pseudo-deltidium ; while in the 
middle of the ventral one there exists a prominent V-shaped cardinal process. 
The ventral valve is moderately convex, and flattened towards its aurieulate 
cardinal extremities. The beak, which is small and incurved, does not overlie 
the hinge-Une ; while the dorsal valve assumes in different specimens a greater 
or lesser degree of concavity, and foUows the curves of the opposite one. 
Exteriorly the surface of the ventral valve is covered with numerous small 
thread-like radiating strise, which increase in number by occasional bifurcation, 
or interstriations at various distances from the beak, so that as many as one 
hundi'ed and twenty ribs may be counted round the margin of certain specimens, 
while at irregular distances small spines projected from the rounded surface of 
the striee. In addition to these, on each side of the beak there exists along the 
cardinal edge from five to nine slanting tubular spines, which become longer 
and larger as they approach the extremities of the cardinal edge. The surface 
of the dorsal valve is striated as in the ventral one ; and minute perforations 
or punctures may be perceived over the entire surface of the shell, and which 
are the exterior orifices of the canals which traverse the shell, as in Productus. 
In the interior of the ventral valve there exists a tooth on each side of the 
small fissure, and which fitted corresponding sockets in the opposite valve, 
while the occlusor and divaricator muscular impressions are very similar to 
those of Prodticius giganteus, but proportionately much smaller, as may be 
seen by a glance at the figures of the two species. Under the cardinal pro- 
cess, in the interior of the dorsal valve, a mesial ridge or plate extends to 
nearly two-thirds of the length of the valve, and on either side may be obsei-ved 
two weU defined occlusor muscular scars, the four being comparatively larger 
or more spread out than is generally the case with Productus ; while outside, 
and in front of these, are situated the reniform impressions. 
Chonetes Ilardrensis is a small species, rarely attaining in Scotland eight lines 
in length by twelve in width. It varies, likewise, in the number of its strise, 
and these are very much finer or coarser in some specimens than in others. 
A small variety, whicli I take to be the same species (pi. ii., fig. 7), occurs 
by millions in certain localities, such as at South Hill, Campsie, in a bed of 
shale on the horizon of the Hosie limestone of the Carluke section ; and are 
associated with Sp. Urii in almost equal abundance. The striationin this small 
Chonetes is generally so fine that it can hardly be distinguished without the 
help of a lens ; and although it has been thought that this little form might 
constitute a distinct species, I am still inclined to view it simply as a small 
variety of C. Ilardremis. 
The determination and study of the present species has given me much 
trouble ; and although I have spent much time in the endeavour to arrive at a 
satisfactory conclusion, it is not without some hesitation that the term Har- 
drensis is here provisionally retained ; provisionally, because I am at present 
unable to determine whether Phillips' Devonian shell is the same as that to 
which Schlotheim in 1820 applied the denomination Sarcinulata, as Prof, de 
Kouinck's illustrations of this last differ so much from those given by Prof. 
Schnur and some other palaeontologists. I am likewise uncertain whether 
J. de C. Sowerby's Lept. sordida (1840) be really a synonym of the last-named 
shell, or different from Phillips' Ilardrensis, as has been stated to be the case 
by some aul hors ; and lastly, because my learned friend. Prof, dc Koninck, 
who has paid so much attention to the species of the genus, maintains a dif- 
ferent opiuion to that here recorded, but not absolutely denying the possibility 
of mine being correct. 
