232 



THE GEOLOGIST. 



who has seen Crania alive, has distinctly stated that " The valves open hy mov- 

 ing upon the straight side as on a hinge, without sliding of the valves but 

 it would be out of place and presumptuous were I to dwell any longer upon 

 this contro versed question, my object having been attained if I have been able 

 to lay before the geological and palasontological reader the views of two 

 such eminently distinguislied anatomists as Mr. Hancock and Dr. Gratiolet and 

 no doubt time will prove which is the correct 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 Lingula is found alive, to notice whether 

 or not the valves do slide upon one another. "We will now conclude the little 

 we had deemed necessary to say of the animal by observing that the oral arms 

 are not supported as in many of the articulated genera by a more or less com- 

 plicated system of lamellse ; that they are fleshy, with their spires directed 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. squamiformis, L. Scotica, L. mytiloides — ^not- 

 withstanding that palaeontologists believe in the existence of a large number. 



XLYI. — Liis^GULA SQUAMiFOEMis. Phillips. PI. v., fig. 30-35. 



Lingula squamiformis. Phillips' " Geol. of Yorkshii-e," vol. ii., pi. xi., fig. li, 

 1836, = L. Portlocki, 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 slightly angular at its extremity in the dorsal valve, with 

 a thickened margin, tapering pointed retraUy at its termination in the ventral 

 one, which is consequently so much longer than the opposite valve. The valves 

 are slightly convex, but somewhat depressed along their middle. In tlie dorsal 

 one there exists a small apex close to the rounded margin of the beak, and from 

 which usually radiate three small rounded ridges, separated by shallow sulci. 

 The external surface in both valves is covered with numerous fine concentric 

 striee, or Ihies of growth, giving to the shell a beautifully and delicately sculp- 

 tured appearance, for the minute pKcations of growth succeed each other with 

 much regularity, while some stronger lines or interruptions in growth are pro- 

 duced at varialjle 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 couimon species in certain Scottish carboniferous strata and 

 localities, and can be distinguished from its congeners by shape and sculptiu-e, 

 altliough the Silurian Lingula granulafa of Phillips approaches it nearest both 

 in shape and sculpture ; this last is, however, usually less elongated, and does 

 not jn-escnt tliose radiating ridges, which are generaily but not always observ- 

 able in the carboniferous species. In liis 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 u])per Palaeozoic rocks, the more elongated narrow oblong species, well 

 ligurcd in Porllock's ' Geological Report,' tab. 32, fig. 5, under this name, 

 might be called L. Vorllocld (M'Coy), its proportional width is only 5 5-1 00th 

 in the long, and (jO-lOOtli 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 per- 

 lectly similar to many of the Scottish examples of the species, but was not very 



