232 
THE GEOLOGIST. 
who lias seen Crania alive, has distinctly stated that " The valves opeu by mov- 
ing upon the straight side as on a hinge, without sliding of the valves;" but 
it wo\ild be out of place and presumptuous were I to dwell any longer upon 
this coutroversed question, my object having been attained if I have been able 
to lay before the geological and palroontological reader the views of two 
such eminently distinguished anatomists as Mr. Hancock and Dr. Gratiolet and 
no doubt time will prove which is the coiTect interpretation ; for now that the 
question at issue has been made known, it will not be difficult for some ob- 
server, who may happen to be where Lincjula is found alive, to notice whether 
or not the valves do slide upon one another. "VVe will now conclude the little 
we had deemed necessary to say of the animal by observing that the oral arms 
are not supported as m many of the articulated genera by a more or less com- 
plicated system of lamella; ; that they arc fleshy, with their spires dkeeted in- 
wards towards each other. 
After having assembled and compared with much attention a very great 
many specimens of Scottish Carboniferous Lingula, I could conscientiously 
admit or distinguish but three — L. squamifonnis, L. Scotica, L. mi/tiloides — not- 
withstanding that palaeontologists believe in the existence of a large number. 
XL VI. — Lingula squAMiroiiMis. riullips. PI. v., fig. 30-35. 
Lingula sqi'.amiformit. Phillips' " Geol. of Yorkshu'e," vol. ii., pi. xi., fig. 14, 
1S36, = L. PortlocM, M'Coy. 
The shells composing this species are longitudinally oblong, one-third, or less, 
longer than wide, with sub-parallel sides, and broadest towards the anterior ex- 
tremity ; the frontal margin assuming either a very slight inward or outward 
curve. The anterior portion is gradually curved on either side ; the beak 
being rounded, or but sb'ghtly angidar at its extremity in the dorsal valve, with 
a thickened margin, tapering pointed retrally at its termination in the ventral 
one, which is consequently so much longer than the opposite valve. The valves 
are shghtly convex, but somewhat depressed along their middle. In the dorsal 
one there exists a small apex close to the rounded margin of the beak, and from 
which usually radiate three smaU rounded ridges, separated by shallow sulci. 
The external surface in both valves is covered with numerous fine concentric 
stria;, or hues of growth, giving to the shell a beautifully and delicately sculp- 
tured appearance, for the minute plications of growth succeed each other with 
much regularity, while some stronger lines or uiterruptious in growth are pro- 
duced at variable distances. The internal muscular impressions are well 
defined in some specimens, especially those produced by the occlusor and ex- 
ternal adjustors of Hancock. 
This is a counnon species in certain Scottish carboniferous strata and 
localities, and can be distiugmslicd from its congeners by shape and sculpture, 
although the Silurian Lingula gramdata of Pliillips approaches it nearest both 
in shape and sculpture; this last is, however, -usually less elongated, and does 
not present those radiating ridges, which are generally but not always observ- 
able in the carboniferous species. In his work on British Palaeozoic fossils. 
Prof. M'Coy concludes his description of L. squamiformis by stating that " the 
wide, short, oblong form of this species easily distinguishes it from the others 
in the upper Palaeozoic rocks, the more elongated narrow oblong species, well 
figured in Portlock's ' Geological Report,' tab. 32, fig. .5, under this name, 
might be called L. Portlocki (M'Coy), its proportional width is only 55-lOOtli 
in the long, and 60-lOOth in the short valve ;" but specimens connecting the 
narrow and the wider varieties are so numerous that I could not admit the two 
extremes as distinct species, besides which, Phillips' original example is pei'- 
fectly similar to many of the Scotti.sh examples of the species, but was not very 
