CARBONIFEROUS BRACIIIOPODA. 
305 
It is to me quite evident from the varied manner in wliicli the surface of the shell of 
the dorsal valve is either closely or sparingly covered with tubular spines, that 
the function of these spines may be differently explained. In some species, such 
as in Produdus 'proboscideus, P. co^nplectens, and others, it is clear that the shell attached 
itself to foreign bodies by some of its spines, as described by Mr. Etheridge, jun. In 
some species, such as in Productus sinuatus^ P. striatus, the spines are chiefly 
restricted to the vicinity of the cardinal ridge, and stand out perpendicularly to the 
surface of the valve. In other species, such as P. fmibriatus^ they are tolerably 
regularly disposed in concentric lines over the surface of the valve ; and in other species, 
such as P. mesolohus, P. Jmmerosus, P. longispinus, &c,, they are few in number, very 
widely scattered, while in the first-named hardly any are to be seen. In such species as 
P. punctatus, &c., they closely invest the surface of the valve, like a head of hair, but 
arranged in wide bands, a narrow smooth space occurring between each successive band ; 
while in P. spinulosus they are short and arranged in a regular manner over the whole 
surface of the dorsal valve. In many species, such as in Prod, aculeatus, they are of 
great length, more numerous and more erect near the cardinal extremities. In some 
forms they stand out perpendicularly from the surface of the shell, while in others again 
they are closely adpressed to its surface. 
It seems to me very probable that, while some forms were able to attach themselves 
by means of their cardinal spines, the larger number of species did not make use of 
them for that purpose. Some of the species in all probability lay on soft muddy 
bottoms on their larger or ventral valves; and this was evidently the case in Prod. 
Liang ollensis, P. giganteus, and other species which possessed very thick and massive 
ventral valves, and very thin dorsal ones : and the hollow spines in some forms may have 
helped them to steady themselves on the soft bottom on which they lived, the immensely 
long and spread out spines of P. semireticulatus leading to that conclusion. It is, however, 
difficult to conceive how P. longispinus, with such dehcate spines, sometimes two or three 
times the length of the shell, and standing out almost perpendicularly from its surface, 
could protect them from injury if the shell lay on its ventral valve ; and I am informed 
by Mr. J. Neilson, that at Joppa, near Edinburgh, there is a bed with thousands of 
specimens of Prod, latissima in which the dorsal or concave valve is downmost, that he 
searched in vain for a specimen lying on its convex or ventral valve, and that he believes 
Mr. J. Thomson found a similar bed at Arran. It is not very often, however, that we 
can procure examples of Productus with their spines in a perfect condition ; but some 
cases do exceptionally occur, for Mr. J. Thomson and Mr. J. Smith, of Stobs, 
Kilwinning, in Scotland, have recently sent me silicified specimens of Prod. acideatiiSy P. 
longispinus, P. muricaius, and Sp. spinulosus, in which every spine was perfectly preserved in 
its place. These remarkable specimens, of which I give some illustrations in PI. XXXVI, 
figs. 10, 11, 14, occur in the top part of the bottom hmestone at Cunningham, Baidland 
Dairy, where the limestone band is twenty-nine feet in thickness. The limestone, being 
