DAVIDSON — SCOTTISH CAUBONIPRROUS lilUCUIOrODA. 
105 
Family I'RonucTiD^. 
Ill tlie second voliinio of the " Ghologist" the cliaractcrs of tlie Vrodiictidm 
have been fully described and illustrated, we will, tlicrefore, <,'enerally observe 
that this family has l)(!cn divided into four genera, or sub-gencra, Frodudm, 
Aiilodeges, Slroplialoua, and Chouetex, but that, as they all bear too natural and 
intimate a relation towards each other, and that 1 he characters brought forv^^ard 
for separating or distinguishing the four groups above named are of somewhat 
questionable value or importance, I am disposed to consider that Aulostegca, 
Strophalosia and Cliotietcs cannot be regarded as more than sub-genera or modi- 
fications of Productus. No calcified processes exist for the sujiport of the oral 
arras. In the Carboniferous rocks of Scotland Produclun and Chuueles alone 
have been hitherto discovered. 
Genus Pboductus. Sowerby. 1814. 
Fifteen or sixteen species of Productus have been found in Scottish Car- 
boniferous strata, and which have been chiefly distinguished by their external 
shape and sculpture, for of the larger number no interiors have been hitherto 
procured. The interior details appear to vary but little, but there exists some 
small marked dissimilarities in certain species, and in order to avoid unnecessary 
repetitions, we wiU at once notice their general features. 
In Prodiidns the internal surface of the ventral valve is concave, a narrow 
mesial ridge, originating, under the extremity of the beak, separates two 
elongated ramified or dendritic impressions which are attributed to the adductor 
or occlusor muscle ; and abnost on a level, immediately under or above, but 
outside of these, there exists two deep longitudinally striated subquadrate iin- 
fressions, which are in all probability due to the carclinal or divaricator muscles, 
mprcssions referable to adjustor and pedicle muscles have not been hitherto 
found, although Mr. Hancock is of opinion that adjustor muscles must have 
existed and been arranged, so as to keep the valves adjusted to each other, and 
thus to have acted as a substitute for the regularly articulated hinge, wiiich is 
certainly absent, if not in all (?) at least in the generality of known species. 
The only points remaining to be noticed in connection with this valve are the 
deep concave sub-sj)iral depressions visible in the interior of some thick shelled 
Producti, such as P. yiganteus, and hoUows which were probably occupied by 
the spiral arras. 
The internal surface of the dorsal valve is more or less convex, sometimes 
abnost flat, and presents in the middle of the hinge-line a prominent bilobed, or 
trilobed projection or cardinal process, whose upper surface having afforded at- 
tachment to the cardinal, or divaricator muscle. Under this a narrow longi- 
tudinal ridge, or septum, generally extends to about half (or more) of the 
length of the valve, and on cither side are seen the ramified, or dendritic im- 
pressions which we consider to be attributable to the adductor, or posterior 
and anterior occlusor muscles ; these are at times situated so close toget her on 
either side of the median ridge, as to render the quadruple attachment not so 
distinct as could be desired, but they are well defined in some valves of Pro- 
ductus lonpispiuas, as may be seen by a reference to fig. IG of our plate II. Out- 
side, and in front of the muscular scars above described are the two " reniforin 
impressions." Their surface is generally smooth ; they are bounded with 
ridges, and after dividing the occlusor muscles, proceeded in an oblique and 
almost horizontal direction, then turning abruptly backwards, terminate at a 
short distance from their origin. There exists also in many species, but not in 
all, two prominences, one on each side of the median ridge, and close to the 
base of the nurscidar scars. The internal sui-face of Productus is covered with 
innumerable granulations and spinose asperities. The shell itself being likewise 
VOL. HI. 0 
