CARBONIFEROUS BRACHIOPODA. 
30;} 
34. Productus complectens, B. Mherid(/e,jun. Dav., Sap., PI. XXXV, figs. 4 — 18. 
Pkoductus complectens, B. Etheridge. Quart. Journ. Geol. Soc, vol. xxxii, p. 45-4, 
pis. xxiv and xxv, figs. 1 — 24, 1876, and 
vol. xxxiv, p. 498, 1878. 
Shell very small, nearly as broad as long. Dorsal valve semicircular, with strong, 
undulating, concentric, often interrupted wrinkles or corrugations. Ventral valve deeper 
than the opposite one, adhering by its spines to foreign bodies. Hinge-line straight, and 
about as long as the breadth of the shell ; beak small. Length from less than a line in 
diameter up to more than two lines. 
Ohs. — This small shell has been minutely described and illustrated by Mr. Robert 
Etheridge, jun., in the ' Quarterly Journal of the Geological Society,' wherein he 
shows that the spines were wound round the bodies of attachment, chiefly to small 
Encrinite stems and fragments of Polyzoa, but generally to the former, and in the most 
complete manner, holding on by two or more of its spines, and that when the organism to 
which the Productus was attached was of larger size than the latter the whole of the ventral 
valve was applied to it, the spines spreading out and round on each side ; but when the 
foreign body was of less diameter than the Productus, as was usually the case with frag- 
ments of Polyzoa, several of the spines were wound tightly round, especially near the beak, 
and the remainder of the valve remained free. He observes, likewise, that the attachment 
took place during the life of the Crinoid ; for, in nearly every case where the Productus 
remains adhering we find the rate of growth was less than that of the Crinoid, the result 
being that the substance of the latter surrounded or enclosed its parasite first, the 
encircling spines disappearing, and gradually the shell. We have, he further adds, 
specimens showing this remarkably well in all stages of the process, from the mere 
absorption of the spines by the substance of the Crinoid up to the total disappearance of 
the Productus itself, when the Crinoid stem assumed a swollen and distorted appearance. 
The number of concentric corrugations, both in the dorsal and ventral valves, were very 
variable, and comparatively for so small a shell very wide, and strong. Mr. Etheridge 
observes, also, that they were in the dorsal valve, perhaps, fewer, and more numerous than 
in the ventral valve, the spines being irregulaiiy scattered over the surface of the valves, 
a row of prominent, strong spines occurring along and immediately below the hinge-line 
of the ventral valve. 
Hab. — Mr. Etheridge informs us that his Productus occurs abundantly in the Lower 
Carboniferous Limestone Group of Scotland ; that it is found at Skateraw Harbour, and 
East Barns Quarry, near Dunbar, in shale over the second Limestone Hosie Lime- 
stone) of the Midlothian series, and in this limestone it was collected by Mr. James 
Bennie, of the Scottish Geological Survey. The same collector obtained some well- 
