110 
THE GEOLOGIST. 
smaller variety or synonym ; P. neitiifetinilatus, and its variety Martini is one of 
the commonest speeics of the g-cnus we find iu Scotland. 
In Lanarkshire it .las been collected in sciveral stages ; tlius, in the parish of 
Carlnke, at Braidvvood-meadow, it is found at three hundred and seventeen 
fatlioms below the "Ell coal," three hundred and forty-three at Langshaw 
Burn, three iiundred and seventy-llvc at Mossidc and Nellficld, three hundred 
and ninety-one at Braidwood Gill. It occnrs also at Brockley, Birkwood, and 
Middleholm, near Lesmahago ; Calderside, East Kilbride ; on the east bank of 
the Avon, near Strathavon ; and Robroyston, north of Glasgow. In llenfrew- 
shire, at Arden- and Orchard-qnarries, Thornlicbank ; Barrhead and Howood, 
near Paisley. In Ayrshire, at Boughwood and West Broadstone, Bcith ; 
Aucheuskeigh, Dairy ; Goldcraig and Monkredding, near Kilwmning ; Cessnock, 
parish of Galston ; Xethcrnewton, parish of Loudon ; Craigie, near Kilmar- 
nock. In Dumbartonshire, at Netherwood and Castlecary. In Stirlingshke 
it occurs in several stages, such as Craigenglen, Balglass Burn, Mill Burn, 
Balgrochan, Campsie main-limestone and ironstone, black limestone and shale 
of South Hill (Campsie), Balquarhag-e and Corrie Burn. It has also been col- 
lected iu Bute, iu Eifeshire, and in the Lothians. 
XXIX. — Pkoductus longispinus. Sowerby. PI. 2, figs. 10-19. 
Produetus longiapinm, Sowetby, Min. Con., vol. i., p. 154, pi. Ixviii., fig. 1, 
1814, = i*. Fleminyii, Sow., = P. spinosus, Sow., = P. lohattis. Sow., etc. 
The shell we are about to describe somewhat resembles P. semiretirulatus, 
but is always a much smaller species, and well distinguished by some of its in- 
terior details. It is usually slightly transverse, but sometimes, though more 
rarely, a little longer than wide, the hin"-e-line being 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, eonnneneing at a short distance from 
the extremity of the rounded and incurved beak, becomes wider and deeper as 
it approaches the frontal margin ; the auriculate cardinal expansions are small 
and slightly wrinkled, while the entire surface of the valve is covered with 
numerous small radiating romidcd striae, tolerably regular in their course and 
respective width, but augmenting in number here and there by the means of 
occasional bifurcation and intercalation. A few irregularly scattered and very 
long slender tabular spines project from some of the ribs, and are niore numerous 
on or near the auriculate expansions. The dorsal valve is concave, with a 
small mesial roimded elevation towards the frontal margin ; its surface is striated, 
as we have already described for the ventral one, both valves being likewise 
marked vnth. small concentric undulating wrinkles on the beak, and to some 
distance from the hinge-Une. Beautifully perfect interiors of both valves are 
not very rare in certain localities. On the concave surface of the ventral one, 
two elongated contiguous dendi'itie ocelusor impressions project at times con- 
siderably above the level of the valve, and immediately under but outside of 
these may be seen the two large longitudiuaUy striated subquadrate impressions 
attributable to the divaricator muscle. A glance at our figures of this and at 
the corresponding valve of P. senureticulatus will explain better than could be 
done with words the difference in position occupied by these muscles in the two 
species. The occlusors in the last-named shell are almost upon a level and longi- 
tudinally parallel with the divaricators ; while in P. longiq)iHus the divaricators 
commence only at or close to the base of the oeelusors. A ditlcrcnce in the 
arrangement of these muscles occurs likewise in P. puncf.afm, and denotes that 
the tlu-ee species might be distinguished alone by the details connected with 
these interior arrangements, and hence the importance of seeking for the 
interiors of those species of wliich we do not possess — the detached valves, or 
