CAMBRO-SILURIAN FOSSILS. 229 



shorter valve. In the L. quadrata also the front is much rounded 

 and narrower, and the rather strong mesial lineation of the de- 

 corticated specimens does not occur in our species, in which, 

 when the surface is removed, there are only seen traces of obso- 

 lete, broad, longitudinal fibrous bands, not at all confined to the 

 middle of the shell, nor linear in character. As usual in fossil 

 LingulcBy it is the beak only of the smaller valve which is seen 

 most commonly ; but two of our specimens show the pointed beak 

 of the larger valve, extending a quarter of an inch beyond the 

 rostral margin of the other, the two being undisturbed from their 

 original position. 



Common in the sandy and calcareous schists of Alt yr Anker, 

 Meifod, Montgomeryshire ; sandy schists of Das Eithin ridge, 

 Hirnant, Montgomeryshire. 



(Col. University of Cambridge.) 



Spondylobolus (M'Coy), n. g. 



Gen. Char. Suborbicular, slightly narrowed towards the indi- 

 stinct, short hinge -line, nearly equivalve, flattened ; small valve 

 with a slightly excentric apex, beneath which, on the interior, 

 the substance of the valve is thickened into a wide undefined 

 boss ; opposite valve slightly longer, from the apex being per- 

 fectly marginal and slightly produced, channelled by a narrow 

 triangular groove, the anterior end of which is flanked within 

 by two very prominent thick conical shelly bosses, represent- 

 ing hinge-teeth : substance of the valves thick, testaceous, not 

 glossy, minutely fibrous, but not distinctly punctured under a 

 lens of moderate power, except by the ends of the fibres. 



One species of this genus is indistinctly known already from 

 the figures and descriptions of Mr. Davidson under the name 

 Crania Sedgwickii, the prominent cardinal protuberance being 

 taken for the posterior pair of muscular impressions ; neither the 

 tissue of the shell nor the internal impressions, however, are 

 identical with those of Crania. The grooving of the beak* of 

 one valve, and the depress?d orbicular form, show the strongest 

 affinity to the Russian genus Obolus, which differs however by 

 its glossy corneous substance, pecuhar internal impressions (as 

 figured by Kutorga), and want of the conical cardinal bosses. 

 These latter, as well as the termmal beak of one valve and sub- 

 central beak of the other, remind us of Trematis of Sharpe ; but 

 neither of the specimens I have examined of the small valve show 

 the fissure of that genus, nor does Mr. Davidson allude to any- 



* Although this is not seen in the pubUshed figure of the C. Sedgwickii, 

 I detected it in the original specimen, which, however, has been obscured 

 by too much clearing with the knife. 



