CARBONIFEROUS BRACHIOPODA. 
307 
36. Productus Llangollensis, Dav. Carb. Mon., p. 277, PI. XLV, figs. 1 — 6; 
and PI. LV, figs. 9,10. 
Since publishing my description of this very remarkable species, Mr, John Aitken has 
added some few additional details in a paper of his " On Prod/ictus Llangollensis, from 
the Eglwseg Rocks, Llangollen, North Wales," 1869. He states that the species occurs 
very abundantly in a black calcareous shale, near the base of the Lower Carboniferous 
Limestone at the Eglwseg Rocks, near Llangollen. "The bed of shale in question is 
about three feet in thickness, of a dark-grey colour and fine texture. Throughout the 
entire body of these shales the shells are profusely distributed without any apparent 
order or stratification, and lie in various positions and at all angles ; the margins 
of the shells are frequently broken, a circumstance which Mr. Davies, of Oswestry 
(who has paid considerable attention to the Carboniferous Limestone of North Wales, 
and its contained organic remains), considers furnishes evidence of their having been 
drifted from a distance to their present resting place. I, however, entertain serious 
doubts as to the correctness of this inference, having failed to discover the least trace of 
attrition on the surface of the shells, the indications of which must inevitably have been 
left had they been subjected to the action of a current of water sufficiently powerful, not 
only to overcome the resistance to motion presented by heavy bulky bodies, but also to 
have violently fractured their immensely strong and massive shells. I would rather look 
to the pressure to which the soft, yielding, muddy matrix was subjected subsequent to 
the entombment of the fossils, in consequence of the gradual accumulation of the super- 
incumbent mass of Carboniferous Limestone, as a probable explanation of their being so 
often in a broken state." 
37. Producttis semireticulatus, Martin, sp. Dav., Carb. Mon., p. 149, PI. XLIII, 
figs. 1— 11 ; and PI. XLIV, figs. 1—4; 
Sup., Pi. XXXV, figs. 1, 2, and PI. XXXVI, 
figs. 12 and 17. 
Since I described this species Mr. John Young has discovered in the Lower Car- 
boniferous Limestone of West Broadstone, Beith, Ayrshire, specimens of Productus 
semireticulatm with numerous attached spines of extraordinary length. A specimen 
measuring one inch and three quarters in breadth had spines some five inches in length, 
imperfect at their ends, and evidently longer once. These hollow spines, one line in 
breadth, have their sides subparallel, tapering very little, and are remarkably shiny 
40 
