DAVIDSON — SCOTTISH CARBONIFEROUS BRACHIOPODA. 107 



convex or gibbous, the cardiual angles being generally prolonged or extended 

 in the shape of auriculate expansions, semi-cylindrically enrolled, and gradually, 

 or more or less abruptly separated from the gibbous portion, or body, of the 

 shell ; the beak is large, rounded, and often greatly incurved, but not always 

 overhanging the hinge-line. This valve is also either evenly convex or ii-regu- 

 larly, and more or less deeply furrowed, the surface being likewise covered with 

 a vast number of longitudinal flexuou.s strise, which vary somewhat in thickness 

 according to age and specimen, tliree or four generally occupying the width of a 

 line towards the middle or margin of the shell ; these little ribs are also frequently 

 confluent, bifurcating, or suddenly disappearing, increasing in number as they 

 approach the marginal portions of the shell, and at short intervals giving birth 

 to short spines, or spinulose asperities, which were more numerous and larger 

 upon the auriculate portions of the valve. The dorsal valve is concave, 

 generally following the curves of the opposite valve, somewhat concentrically 

 wrinkled near the hinge-line, and longitudinaly striated in a very similar man- 

 ner to what we have described for the ventral one. It will not be necessary 

 to describe the interior with any detail, since the general description already 

 given, as well as the figures of our plate, ^vill sufiiciently illustrate all the 

 characters ; bat we may notice the great tliickness of the ventral valve com- 

 pared with that of the dorsal one, which is usually thin. The ventral valves 

 of all species of 'Product us do not possess that extraordinary thickness which 

 admit of those deep subspiral hollows for the accommodation of the spiral arms, 

 which are visible in the present forms. The divaricator muscular scars are 

 here immediately under and outside of the occlusor ones, while in Productus 

 longispinus and some other species, the devaricator impressions are almost upon 

 a level with the occlusor ones. In the dorsal valve the cardinal process 

 (which varies much in shape, according to the specimens and age of the indi- 

 vidual) is usually trilobed, its V-shaped upper suiface is usually striated, the 

 other impressions are clearly defmed in the figure. 



This is certainly the largest species of the genus at present known, some 

 English examples having attained six inches and two lines in length by eleven 

 inches four lines in width; and although no Scottish examples have, to my 

 knowledge, attained similar proportions, some have measured five and a-half 

 inches in length by nine or ten in width. 



Productus giganteiis characterises some of the lower stages of the Car- 

 boniferous system wherein Brachiopoda have been found ; thus at Braidwood 

 Gill, in Lanarkshire, it is found for the first time at three hundred and ninety- 

 seven fathoms below the horizon of the " Ell Coal." 



In Stirlingshire it occurs in the MiU-Burn beds, Campsie. It was likewise 

 collected in the island of Arran, by Prof. Bamsay, and in red limestone at Close- 

 burn, in Dumfriesshire, by the late Dr. Eleming. In Edinburgshire, at Joppa. 

 In Haddington, at Cat Craig, near Dunbar. In Peebleshire, at Carlops, etc. 



XXYII. — Peoductus latissimus. J. Sowerby. PL ii., figs. 8-9, and pi. iv,, 



fig. 26. 



Productus latissimus. J. Sowerby, Min. Con., vol. iv., p. 32, pi. 330, 1822. 

 The shells composing this species are very transversely elliptical or spindle 

 shaped, with a long straight hinge-line, and are completely deprived of area, 

 the breadth being more than twice as great as the length ; the ventral valve is 

 also very convex forming in profile more than a semicircle ; the beak large and 

 much incurved, while the passage from the gibbous body of the valve into the 

 auriculate expansions or ears is so gradual as to be more often insensible, and 

 does not appear in the many examples that have passed under my inspection to 

 have ever i)een so sharply separated, or defined, as is usually the case with P. 

 giganteus ; it is also much more transverse, or elliptical, than is the last named 



