110 



THE GEOLOGIST. 



smaller variety or synonym ; P. semireticulatus, and its variety Martini is one of 

 the commonest species of the genus we find in Scotland, 



In Lanarkshire it jas been collected in several stages ; thus, in the parish of 

 Carluke* at Braidwood-meadow, it is found at three hundred and seventeen 

 fathoms' below the "EU coal," three hundred and forty-three at Langshaw 

 Bum, three hundred and seventy-five at Mosside and Nellfield, three hundred 

 and ninety-one at Braidwood Gill. It occurs also at Brocldey, Bii'kwood, and 

 Middleholm, near Lesraahago ; Calderside, East KUbride; on the east bank of 

 the Avon, near Strathavon ; and Robroyston, north of Glasgow. Li Renfrew- 

 shire, at Arden- and Orchard-quarries, Thornliebank ; Barrhead and Ho wood, 

 near ' Paisley. In Ayrshire, at B.oughwood and West Broadstone, Beith ; 

 Auchenskeigh, Dairy • Goldcraig and Monkredding, near KUwimiing ; Cessnock, 

 parish of Galston Nethernewton, parish of Loudon; Craigie, near Kilmar- 

 nock. In Dumbartonshire, at Netherwood and Castlecary. In Stirlingshire 

 it occurs in several stages, such as Craigenglen, Balglass _ Bnj-n, Mill Burn, 

 Balgrochaii, Campsie main-lunestone and ironstone, black limestone and shale 

 of South lini (Campsie), Balquarhage and Corrie Burn. It has also been col- 

 lected in Bute, in Eifeshire, and in the Lothians. 



XXIX. — Prodtjctus LOifGispiNUS. Sowerby. PI. 2, figs. 10-19. 



Produd'us longisj)imiH, Sowerby, Min. Con., vol. i., p. 154, pl. kviii., fig. 1, 

 1814, = P. Flemingii, Sow., = P. spinosus, Sow.;, = P. lobafus. Sow., etc. 



The shell we are about to describe somewhat resembles P. semireticuJatiis, 

 but is always a much smaller species, and well distinguisbed by some of its in- 

 terior details. It is usually slightly transverse, but sometimes, thougb more 

 rarely, a little longer than mde, the hinge-line beiiig about as long as the 

 greatest width of the shell. The ventral valve is convex, and at times gibbous, 

 with or without a mesial sinus, which, commencing at a short distance from 

 tlic extrcmily of the rounded and incurved beak, becomes wdder and deeper as 

 it aj)proachcs the frontal margin ; the auriculate cardinal expansions are smaU 

 and slightly wrinkled, wbile the entire surface of tbe valve is covered with 

 numerous small radiating rounded striae, tolerably regular in their course and 

 respective width, but augmenting in number here and there by the means of 

 occasional bifui'cation and intercalation. A few irregularly scattered and very 

 long slender tabular spines project from some of the ribs, and are more numerous 

 on or near the auricubitc expansions. The dorsal valve is concave, with a 

 small mesial rounded elevation towards the frontal margin ; its surface is striated, 

 as we luivc abready described for the ventral one, both valves being likewise 

 niark(!d with snudl eoneeutric undulating wiinldes on the beak, and to some 

 distance from the liini;\'-liiu\ iH-autifully perfect interiors of both valves are 

 not very rare in cevtaiu localities. On the concave surface of the ventral one, 

 two elongated contiguous d luliitie ocelusor impressions project at times con- 

 siderably al)ovc the level of the valve, and immediately under but outside of 

 tiiese may be seen the t\\ (^ hru'c longitudinally striated subquadi'ate impressions 

 atlril)utable to the divaricMtoi- muscle. A glance at our figvuTs of tliis and at 

 the eorresponiling valve of P. scuiircfic/ddi/'s will explain better than could be 

 done with wonls the dillVrence in position occupied by these muscles in the two 

 species. The ocelusors in the last -naim\l ^licll arc almost upon a level and longi- 

 tudinally jwallel with the divaricaiors ; m F. Ioi/f/ispi,/i!s ^x-^xiQAiox^ 

 eoninuMU'c only at or close to the base of the occlusors. A diiference in the 

 an-anu:enunit of these muscles occurs likewise in P. p/n/cf(ifi(s, and denotes that 

 llu> (liree siieeies niight be distinguished alone by the details coimeetcd with 

 tlu'se interior arrangements, and^ hence the iniportanee of seeking for the 

 nitenors of those species of wliich wc do not possess — the detached valves, or 



