DAVIDSON — SCOTTISH CARBONIFEROUS BRACHIOPODA. 



109 



Var. A, Producfns semireticidatns, figs. 1-8, is transversely oval, or of a 

 rounded quadrate shape, but it is also at times somewhat elongated, the hinge- 

 line being either rather shorter or as long as the greatest width of the shell. The 

 ventral valve is always gibbous, with and sometimes without a shallow longitu- 

 dinal median sinus, or depression, the auriculate cardhial exjDansions being 

 moderately developed but clearly defined ; the beak is wide and incuiwed, both 

 usually covered with irregular concentric wrinkles, always larger and deeper 

 upon the auriculate expansions, and the entire surface of the shell is covered ^A^ith 

 numerous radiating longitudinal rounded striae, from which project at variable 

 intervals tabular spines of moderate length. The width of the strise, as well as 

 the interspaces between them, varies also accordmg to the specunen, two or 

 more usually occupying the breadth of a line. The larger number are simple, 

 but others bifurcate here and there, and sometimes two or more (in rare cases) 

 will unite towards the margin, so as to form but a single rib, while others are 

 due to intercalation. Several ribs will also at times cluster together, so as to 

 produce an elevation, and thus gi^'ing the frontal portion of the shell a some- 

 what grooved appearance. The spines are likewise more numerous, larger and 

 longer in certain examples than in others, but always most so upon the auriculate 

 portions of the valves. The dorsal valve is slightly concave, or flattened to 

 some distance from the hinge, so that a considerable space was left free for the 

 soft portions of the animal ; the external sculpture is also very similar to that 

 which has been described for the opposite valve. The ventral valve is thicker 

 than the dorsal one ; both become extremely thin and sometimes recurved 

 near their margin. The interior of both valves have been often procured, and 

 in excellent preservation, as may be seen from tlie figures of oui* plate, and we 

 will merely notice that in the ventral valve the occlusor impressions are situated 

 almost upon a level with the divaricator scars, and much lower in the valve 

 than for example in P. giganteus, etc. In the dorsal valve the occlusor impres- 

 sions are often beautifully sculptured, and the cardinal process is trilobed. 



Produdus semireticulatns has sometimes attained large dimensions, a Scottish 

 specimen represented in our plate has measured tAvo inches three lines in length 

 by two and a-half inches in width, and it has elsewhere assumed still larger 

 proportions. P. sulcatus appears to be nothing more than a smaller variety of 

 the same, wherein the median sulcus of the ventral valve is more than usually 

 deepened, and upon the lateral portions of the beak (close to the aui'iculate ex- 

 pansions) there existed sometimes, but not always, a somewhat elevated ridge, 

 with a row of rather large prominent spines. P. Scoticus appears to me to be 

 undoubtedly a variation of shape only of the species under description, and not 

 of P. giga7iteus, as has been supposed by some palaeontologists. I have had the 

 loan of the origmal figured specimens for several months in my possession, and 

 both valves will be found represented in our plate. 



Var. B, or Martini, figs. 10-12, is distinguished from the preceding one by 

 the great length and irregularity of its anterior prolongation ; the arched beak 

 is suddenly bent downwards in an almost straight line, giving to some speci- 

 mens a peculiarly elongated and geniculated appearance. The dorsal valve is 

 slightly flattened to some distance from the hinge-line, when it closely follows 

 the curves of the opposite one. The thinness of the shell sometimes makes it 

 liable to fracture at some distance from the beak, as may be seen in one of the 

 figures ; the lateral portions of the valve are likewise much dilated, with 

 numerous spines sometimes projecting from the auriculate portions of the 

 valve. The beak is concentrically wrinkled, and the entire surface is covered 

 with thread-hke strise, which bifurcate sometimes several times, especially upon 

 the lateral portions of the shell. 



This is the variety to which Martin in 1809 applied the specific denomination 

 of Anomites prodtcctus, and of which Sowerby's P. concinnus is evidently only a 



