CAMBRO-SILURIAN FOSSILS. 211 



separated by rather wider smoother spaces. Length 10 hues, 



greatest width (a httle in front of the middle) 10^ lines, height 



of cardinal area three-fourths of a line. 



In size and general character this agrees with the Pseudocrania 

 antiquissima (Eichw. sp.) as given by M. de Verneuil (Geol. Euss. 

 t. 1. fig. 12), but is easily distinguished externally by the beak 

 being close to the posterior margin, and the remarkable divari- 

 cating sculpture of the valves, and internally by several minor 

 points of detail obvious on comparison with the figure. 



Common in the schists on the Bala limestone at Bryn Melyn 

 quarry; schists of Pont y Glyn, Diffwys ; and in the fine grits of 

 Tan y Craig, Builth. 



{Col. University of Cambridge.) 



Siphonotreta micula (M'Coy). 



Sp, Char. Longitudinally ovate, length and width about equal ; 

 sides and front broadly rounded, with a uniform curve, pos- 

 terior extremity slightly acuminated; gently convex, perfo- 

 rated valve most so; greatest depth about one-fourth the 

 length from the beak, which is near the posterior margin, and 

 perforated by a round tubular opening ; surface marked with a 

 few concentric waves of growth, and sharp, flat, regular con- 

 centric linear strise, about seventeen in the space of one mil- 

 limetre ; several short, slender, conical spines are rather irre- 

 gularly scattered over the surface, the substance of the shell 

 exhibiting under a high power an extremely minute reticular 

 punctation. Average length (of rather large specimen) 2 lines, 

 width usually rather less. 



This small species varies from nearly orbicular to ovato-penta- 

 goual in outline ; in some specimens, particularly those from Well- 

 field, the depressions left by the spines of the surface are very ob- 

 vious and rather crowded, producing a puckered irregularity of 

 the surface, which is not to be seen in most of the specimens 

 from Pen Cerrig ; the concentric lineation is also more distinct 

 in the former, between which the reticular punctation is so excess- 

 ively minute, that it can only be traced with very fine and 

 powerful glasses in favourable lights on the best-preserved por- 

 tions of the shell, differing therefore very much from the most 

 nearly allied fossil, the so-called Terehratula hamifera of Bar- 

 rande. In nearly all the specimens the distinct and rather large 

 circular opening at the apex of the beak is easily seen, and in 

 many specimens an irregular fissure, apparently produced by 

 crushing, extends a variable distance towards the front margin, 

 either in the median line or more or less to one side or the other. 

 The few rather large concentric waves or interruptions of growth 

 are only seen in some specimens. 



o2 



