890 Prof. F. M'Coy on new Cmnbro- Silurian Fossils. 



Abhandlungen, vol. i. p. 418. t. 20. f. 9), but has the reticular 

 punctation infinitely more minute than he describes that of his 

 species to be (half a millimetre long, or four in a square milli- 

 metre). M. Barrande gives the geological place of his species in 

 Bohemia as "gehort der Quartzitetage (D) an d. h. dem am 

 hochsten gelegenen Theile des untern Silurischen Systems von 

 Bohmen/' and the schists in which ours occurs in such profusion 

 in Britain seem to hold precisely the same place. Its gregarious 

 habits are curiously shown by the circumstance of a fragment of 

 shale four or five inches long and wide from Pen Cerrig having 

 afforded upwards of 100 specimens now in the Cambridge col- 

 lection, and another mass not much larger from Wellfield having 

 yielded upwards of 70. 



Very common in certain spots in the black shale of Pen Cerrig, 

 Builth, Radnorshire; and not uncommon in the olive schists of 

 Wellfield, Builth, Radnorshire ; very rare in the olive schists of 

 Pentre Llangynyw near Welchpool, Montgomeryshire. 



{Col. University of Cambridge.) 



Pentamerus microcamems (M'Coy). 



Ref. & Syn. Spirifer'i Icevis, Sow. S. S. t. 21. f. 12 (not Penta- 

 merus lavis, Sow.). 



Sp. Char. Transversely elliptical; receiving valve depressed, gently 

 convex, greatest depth near the beak, which is elevated nearly 

 at right angles, the height' being one-eighth the width of the 

 hinge ; entering valve greatly convex ; beaks small, rather pro- 

 minent, reaching to the plane of the lateral margins, with 

 which the low triangular area is nearly parallel, greatest depth 

 slightly behind the middle ; a broad, faintly marked, slightly 

 convex, obsolete mesial ridge, and a few faint, broad, obsolete, 

 irregular lateral radiations ; hinge-line slightly less than the 

 width of the shell, side margins elliptically rounded, front 

 margins very wide, gently convex ; cardinal area nearly sixteen 

 times wider than high ; surface apparently smooth, or with a 

 very minute fibrous longitudinal striation : internal cast of re- 

 ceiving valve showing the broad triangular boss of the fora- 

 men, shghtly keeled, the mesial septum formed by the junc- 

 tion of its bounding lateral lamellae, only reaching one-third 

 the length of the shell, or little more than equal to the width 

 of the rostral chamber ; cast of entering valve with a very nar- 

 row triangular area in the plane of the lateral margins ; two 

 very slightly diverging dental lamellae, scarcely reaching twice 

 the width of the area (or one-eighth the length of the shell), the 

 exterior edges of which form two more diverging slits, resem- 

 bling cardinal teeth ; a slight indication of a mesial septum 



