BRITISH CARBONIFEROUS BRACHIOPODA. 275 



surface entirely covered with tolerably regular, but more or less interrupted, sub-parallel, 

 concentric ridges or wrinkles. Slender spines rise here and there from the surface of the 

 ventral valve, and are more numerous on the ears. Dorsal valve moderately concave, 

 and ornamented as in the opposite one. 



Average dimensions: length 11, breadth 13 lines. 

 Obs, This Productus appears to be easily distinguishable from the other British 

 Carboniferous species of the genus by its shape and sculpture, and I am supported 

 in this view by Prof, de Koninck, to whom I submitted several specimens. None of the 

 examples hitherto discovered by Mr. Carrington in the Narrowdale Cleft appears to have 

 exceeded the dimensions given above, nor is it near so common as are Ph. Wettonensis, 

 Discina nitida, and Spirifer Carluhiensis. 



Productus or Chonetes comoides, Sow. (p. 180). 



While describing Sowerby's Productus (or Chonetes) comoides, I did not omit to refer 

 to the several difficulties in the way of a satisfactory determination of this important 

 species. I also mentioned that it had been questioned by certain palaeontologists whether 

 the shells (PI. XLV, figs. 1 — G) really belonged to Sowerby's species, and I gave the 

 reasons why I had united them to C. comoides. Peeling, however, uncertain as to the 

 correctness of this view, I requested Mr. D. C Davies, of Oswestry, to kindly endeavour 

 to search for more specimens of the Llangollen form (PL XLV, figs. 1 — G ; PI. LV, figs. 9, 

 10), and especially for examples which would show the interior of the dorsal or smaller 

 valve. Mr. Davies's success was complete in this respect, for at the close of the present 

 summer he forwarded to me seven examples, of which one was a bivalve shell, and of 

 which the valves could be separated (PI. LV, figs. 9, 10). I felt much interested with this 

 important discovery, for the interior of both valves proved in the most satisfactory manner 

 that, notwithstanding the double area and strong articulating hinge-teeth, all the interior 

 dispositions were those of Productus, and this has proved once more that Chonetes, 

 Aulosteges, and Strophalonia, cannot be considered in any other light than sub-genera or 

 section of Productus, and cannot claim generic value. Profiting by Prof, de Koninck's 

 passage through London, I requested him to accompany me to the British Museum, in 

 order that we might have a complete and minute examination of my Llangollen specimens 

 with Sowerby's Prod, comoides and P. hemisphcericus. 



The result of this examination was that we agreed completely that Sowerby's P. hemis- 

 phcericus was nothing more than a modification of age and specimen of Martin's 

 Productus giganteus, as I had already stated it to be at p. 144 of this Monograph, and that 

 it is specifically distinct from P. comoides as well as from the Llangollen form. Prof, de 

 Koninck was, moreover, of opinion that the Llangollen form and P. comoides should be 

 considered as distinct species, and adduced the much larger area, but slightly produced 



