DAVIDSON — SCOTTISH CARBONIFEROUS BRACIHOI'ODA. 
107 
convex or gibbous, tlie cardinal angles being generally prolonged or extended 
in t lie shape of auriculate expansions, scnii-cyhndrically enrolled, and gradually, 
or more or Ic^ss abruptly separated from the gibbous portion, or body, of tlic 
shell ; the beak is largo, rounded, and often greatly ineurvcd, but not always 
overhanging the iunge-line. This valve is also citiier evenly convex or irregu- 
larly, and more or less deeply furrowed, the surface being likewise covered with 
a vast number of longitudinal flexnous strix, whicli vary somewhat ui thickness 
according to age and specimen, three or four generally occupying the width of a 
line towards the nuddle or margin of the slieU ; 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 spundose asperities, which were more nujnerous and larger 
upon the auricidate portions of the valve. The dorsal valve is concave, 
generally following the curves of the opposite valve, somewhat concentrieaUy 
wi-iidclcd near the hinge-line, and longitudinaly striated in a very similar man- 
ner to what we have described for the ventral one. It wdl not be necessary 
to describe the interior with any detad, since the general description already 
given, as well as the figures of our plate, wdl sufficiently illustrate all the 
characters ; but we may notice the great thickness of the ventral valve com- 
pared with that of the dorsal one, which is usually thin. The ventral valves 
of all species of Prodncfus do not possess that extraordinary thickness which 
admit of those deep subspii-al hoUows for the accommodation of the spiral arms, 
wdnch are visible in the present forms. The divaricator muscular scars are 
here immediately under and outside of the occlusor ones, while in Produdus 
loHfi'upinm and some other species, the devaricator impressions are almost upon 
a level with tlie occlusor ones. In the dorsal valve the cardinal process 
(wluch varies much in shape, according to the specimens and age of the indi- 
vidual) is usually trUobed, its V-shajied upper siuface is usually striated, the 
other impressions are clearly defined 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 simdar proportions, some have measured five and a-balf 
inches in length by nine or ten in width. 
Prodiictus gigantem characterises some of the lower stages of the Car- 
boniferous system wherein Brachiopoda have been found ; thus at Braidwood 
GiU, in Lanarkshire, it is found for the first time at tlu-ee hundi'ed and ninety- 
seven fathoms below the horizon of the " EU Coal." 
In Stii'lingsKire it occurs in the Mdl-Bui'n beds, Campsie. It was likewise 
collected in the island of Arran, by Prof. Bamsay, and in red limestone at Close- 
bum, in Dumfriesshire, by the late Dr. Fleming. In Ediuburgshii-e, at Joppa. 
In Haddington, at Cat Craig, near Dunbar. In Peebleshire, at Carlops, etc. 
XXVII. — PaoDTJCTUS LATissiMtis. J. Sowerby. PI. ii., figs. 8-9, and pi. iv., 
fig. 26. 
Produdus lafissinms. J. Sowerby, Min. Con., vol. iv., p. 32, pi. 330, 1822. 
The shells composing this species are very transversely elliptical or spmdle 
shaped, with a long straight hiuge-luie, 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 incui-ved, wlule the passage from the gibbous body of the valve into the 
auricidate 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 been so sharply separated, or defined, as is usually the case with P. 
gigantcus ; it is also much more transverse, or elliptical, than is the last named 
