108 
THE GEOLOGIST. 
shell, the dorsal valve being likewise extiTinely concave, and follows the curves 
of the opposite one. The surface in both valves is coarsely striated, tlie 
flexuous stria; increasing irreguhu'ly by numerous intercalations, and giving 
rise at short interviJs to many small stout spiuulose projections. The striic 
are also proportiouably coarser and more s])inulous than in the last de- 
scribed species, and the shell itself much thinner. In the interior of the 
ventral valve the mxiseular impressions ap])ear to be located nearer the extremity 
of tlie beak than in P. f/if/iiiitois, and in the dorsal valve there ajjpears to exist 
a (lill'erence in the detail of the occlusor muscular impressions, as may be seen 
by comparing the figures we have given of the interior of both species. 
J'/-od//r///,i lafl.ssimns does not apjjear to have ever attained anything like the 
pro])ortious of P. qiqcmieus, for the largest examjilc I have seen did not much 
exceed some two inches in length by four and a-half in width. 
Sowerbv, Phillips, de Koninck, de A^erneuil, and the generality of authors 
have considered the two shells, though closely allied, to be separate species, and 
I am disposed to comcide with their view, although some few palaeontologists, 
and in particular Prof. M'Coy states " positively that the distinctions do not 
really exist ;" and it may be here mentioned tluit, although the two species are 
occasionally found iu the same strata and localities, more often the one form is 
common, where the other is absent. 
In Scotland P. latisnimus is also one of the most characteristic species in 
some of the lower stages of the Carboniferous system. It is found iu Lanark- 
shire at two different levels, thus, at Eelston Burn it occurs at two hundred 
and sixty-five fathoms below " Ell Coal," and three hundred and ninety-one at 
Braidwood Gill, also at Brockley, near Lesmahago. In llenfrewshire at Arden- 
quarry, Thorliebank. In Ayrshire, at Roughwood and West Broadstoue, 
Beitli ; Auchenskeigh, Dairy ; Golderaig and Monkreddiug, near Kilwinning ; 
HaUerliirst, Stevenston ; Nethernewton and Moscow, parish of Loudon ; 
Meadowfoot, near Drunclog and Mullockhill, near Dah-y. In Stirlingshire it is 
known to Mr. Young but from the Craigenglen (Campsie) beds. In Buteshire, 
in the island of Arran. 
XXVIII. — PiiODDCTUS SEMiRETicuLATUS. Martin. PI. iv., figs. 1-12. 
Var. A., Anomites semireticulatns, Martin, Petrif. Derb., p. 7, pi. xxxii., figs. 
1-2, and pi. xxxiii., fig. 4, 1809, = P. anUquatm, Sow., Min. Con., vol. iv., 
pi. cccxvii., figs. 2, 3, 4, = P. Scoticus, Sow., Min. Con., pi. btix., fig. 3, = 
P. sulcatuH, Sow., Min. Con., tab. cccxix., fig. 2, etc. 
Var. B., or Martini, Sow., Min. Con., tab. cccxvii., figs. 2, 3, 4., 1821, = 
Anotiiiten prodndjis, Martin, Petrif. Derb., tab. xxii., figs. 1, 2, 3, 1809, = 
P. concinnm. Sow., Min. Con., tab. eccxviii., fig. 1. 
This species has varied much in its general shape, and I entirely comcide 
with Prof, de Koninck, whUe considering P. semireticulafus, antiqvatns. 
Martini, concinnus, sidcatus, and I wiU add Scoticus, as simple variations 
in shape of a single type or species, for wliich the term semireticulatns has 
been adopted. These varieties are aU so intimately connected by in- 
sensible gradation, that it would often be impossiole to say to which 
in particular certain specimens should be referred. Some palieontologists, 
who do not retam as distinct species aU the names above recorded,* would 
however preserve several of them as varietal denominations ; but after 
the careful examin.ation of a midtitude of specimens, I am disposed to retain 
but two, and which for convenience wdl be here briefly noticed under separate 
heads. 
* There are other synonyms, but which cannot be here recorded. In my Monograph of 
British Carboniferous Brachiopoda full details wJl bo found. 
