108 



THE GEOLOGIST, 



shell, the dorsal valve being likewise extremely concave, and follows the curves 

 of the opposite one. The surface in both valves is coarsely striated, the 

 fh:xuous st ria: iiicr(;asing irregularly by numerous intercalations, and giving 

 rise at short intervals to many small stout spinulose projections. The strise 

 arc also proportionably coarser and more spinulous than in the last de- 

 scribed species, and the shell itself much thinner. In the interior of the 

 ventral valve the muscular impressions appear to be located nearer the extremity 

 of the beak than m P. (jiganteus, and in the dorsal valve there appears to exist 

 a difference 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. 

 rrodiidm latmimus does not appear to have ever attained anything like the 

 pro])ortions of F. giganteus, for the largest example I have seen did not much 

 exceed some two inches in length by four and a-half in width. 



Sowerby, Piiillips, de Koninck, 'de Yerneuil, and the generality of authors 

 have considered the two shells, though closely allied, to be separate species, and 

 I am disposed to coincide 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 that, although the two species are 

 oeeasionally found in the same strata and localities, more often the one form is 

 coimnon, where the other is absent. 



In fSeoi land P. latissimus is also one of the most characteristic species in 

 some of the lower stages of the Carboniferous system. It is found in Lanark- 

 shire at two different levels, thus, at Belston Burn it occurs at two hundred 

 and sixty-five fathoms below "EU Coal," and three hundred and ninety-one at 

 l)r;iidwood Gill, also at Brockley, near Lesmahago. In Benfrewshne at Arden- 

 fjiiarry, Thorhebank. In Ayrshire, at Roughwood and West Broadstone, 

 l^eith ; Auehenskeigh, Daby ; Goldcraig and Monkredding, near Kilwianing; 

 JIallerhirst, Stevenston; Nethernewton and Moscow, parish of Loudon; 

 ^leadowfoot, near Drunclog and MuUockhiU, near Daby. In Stirlingshire it is 

 known 1,0 Mr. Young but from the Craigengleu (Campsie) beds. InButeslure, 

 in the island of jViTan. 



XXVIII. — Productus semireticulatus. Martin. PI. iv., figs. 1-12. 

 Var. A., Anomifes semireticidattis, Martin, Petrif. Derb., p. 7, pi. xxxii., figs. 

 1-2, and pi. xxxiii., fig. 4, 1809, = P. antiqucdus, Sow., Min. Con., vol. iv., 

 rccxvii., figs. 2, 3, 4, = P. Scoticus, Sow., Min. Con., pi. Ixix., fig. 3, = 

 P. siilratiis, Sow., Min. Con., tab. cccxix., fig. 2, etc. 



Var. B., or Martini, Sow., Min. Con., tab. cccxvii., figs. 2, 3, 4., 1821, = 

 JnomifcH prod iw fits, Martm, Petrif. Derb., tab. xxii., figs. 1, 2, 3, 1809, = 

 P. concinnus. Sow., Min. Con., tab. cccxviii., fig. 1. 



This species lias varied much in its general shape, and I entbely coincide 

 with Prof, de Kouinck, while considermg P. semireticidatus, antiqued us, 

 yiartitii, condtnins, ft// /cat us, and I will add Scotici/s, as simple variations 

 in .slia))e of a single type or s])eeies, for which the term serniretic/datus has 

 i)iu'n adopted. _ These varieties are all so intimately connected by in- 

 siMisible gradation, tliat it wouUl often be impossible to say to which 

 in parlie\dar certain specimens should be referred. Some palaeontologists, 

 Nvho do not retain as distinct species all the names above recorded,* would 

 however preserve several of them as varietal denominations; but after 

 the careful examination of a multitude of specimens, I am disposed to retain 

 but two, and which for convenience will be here brieflv noticed under separate 

 heads. 



nJiH-K^I'^.?^ ^r"^^"" p.vnoii,niis, but which cannot be here recorded. In my Monograph of 

 nntmh I nrbomfcrous Umohiopoda luU dctiuls wiU be foimd. 



