TEREBRATULA. 17 



rocks of Wensleydale, Yorkshire ; at Pilsbury Castle, Longnor, Derbyshire, &c. In 

 Scotland Dr. Fleming has the shell from Westlothian. I am not acquainted with any 

 Irish specimens. In Belgium it is stated by M. De Koninck to occur in the lower 

 Carboniferous limestone of Vise, where it is common. 



Terebratula GillingejNsis, Dav. Plate I, figs. 18 — 20; Plate II, fig. I. 



Spec. Char. Obovate, depressed, smooth, slightly indented in front, widest towards 

 the middle, and frontal region. The dorsal valve is convex at the umbone, but thence 

 to within a short distance of the frontal margin presents a straight or even inward 

 curve. The ventral valve exhibits a flatness in the vicinity of the front, so that this 

 portion of the margin is produced, and forms a convex curve, indenting that of the 

 opposite valve. Beak rounded and incurved, projecting beyond the umbone of the dorsal 

 valve ; beak ridges moderately defined ; foramen circular, generally approximating the 

 hinge-line, and partially margined by a small deltidium ; shell-structure minutely perforated. 



Length 9, width 7^, depth 4 lines. 

 7, „ 6, „ 3 lines. 



05s. Numerous examples of this small Terebratula have been collected by Mr. 

 E. Wood, in the Carboniferous beds of Yorkshire. It has been supposed by some 

 palaeontologists to be a variety or young state of Ter. hastata ; while by others it would 

 be referred to the Devonian Atrypa juve?iis of J. de C. Sowerby. We may also 

 notice that, in the work on the 'Palaeozoic Fossils of Devon and West Somerset,' 

 Professor Phillips observes (p. 90), while describing the last-named shell, that, 

 " Mr. Sowerby's figure represents a young specimen ; mine is, perhaps, that of a full- 

 grown individual. It is a well-characterised species, though I have specimens supposed 

 to be varieties of T. hastata, from the mountain limestone of Yorkshire, whose only 

 distinction is that the widest part of the shell is nearer the front, while in Devonshire forms 

 it is nearer the beaks." Sowerby's figure of T. juvenis 1 resembles the young example 

 (PI. I, fig. 20) of our Carboniferous deposits, but from shells of that age it would 

 not be safe to arrive at a conclusion respecting their specific identity, and especially when 

 we find that there exists so much dissimilarity between the adult condition of T. 

 juvenis (as figured by Professor Phillips) and that of our Carboniferous fossil. In the 

 first it is the margin of the dorsal valve that is depressed and convex, while the reverse 

 is the case with the species under description ; it exhibits also that dissimilarity in the 

 relative widest part, as was noticed by Professor Phillips. In the work on the e British 



1 In the 'Trans, of the Geol. Soc.,' 2d series, vol. v, tah. xxxv, Mr. Sowerby describes his Atrypa 

 juvenis — "Broad ovate, slightly convex, smooth, curved, longer than wide; front somewhat pointed; valves 

 nearly equal ; the lower curved upwards with a minute beak. A small, rather flat species, distinguished 

 by its narrow front, and being curved." 



3 



