SPIRIFERID^. 



135 



single species, giving accidental priority to his own designation, while he distinguishes his 

 true T. imbricata by the name T. imbricata, var. abhremata. 



Position and Locality. The exact vertical range of this species has not yet been satis- 

 factorily determined ; and it is uncertain whether it is as extended as that known for 

 A. imbricata. Mr. Salter says that the typical form is a common Caradoc fossil. He 

 finds it in North and South Wales, and in Ireland in Bala shales and limestone. It has, 

 however, been determined by Salter from the Lower and Upper Llandovery rocks of 

 many localities, especially in the Lower at Rhyader, Llandovery, Matherafal, Man- 

 dinam, Welshpool, Haverfordwest, Devil's Bridge, Duffryn Castle, &c. ; and in the 

 Upper Llandovery at Llandovery and Chirbury. It is also found plentifully in the 

 Wenlock Limestone ; at the Wren's Nest, Dudley ; Hay Head, near Walsall ; at Wenlock 

 Edge ; and Benthall Edge, &c. ; in the Wenlock rocks near Carmarthen, Llandeilo, and 

 Pen-y-lan ; also in the Woolhope Limestones of Malvern, Presteign, and East of 

 Walsall. Abroad it occurs in Gothland. 



Atrtpa imbricata, /. de C. Soio. (sp.). PI. XV, figs. 3 — 8. 



Terebratula imbricata, Sow. Sil. Syst., pi. xiii, fig. 27, 1839. 



— MARGINALIS, Burrande. (T. marginalis in tlie description ; T. imbricata 

 in the explanation of plate), Silur. Brach. Bohmen., 

 p. 79, pi. xix, fig. 10, 1847. 

 Ateypa IMBRICATA, Salter. Siluria, 2nd edit., pi. xxii, fig. 19, (the lower figures only). 



[Here A. imbricata is regarded as a variety only of A. margi- 

 nalis.'] 1859. 



Spirigerina — Lindsfrdm. Gottlands Brachiop., p. 362, 1860. 



Spec. Char. Almost circular, often as wide as long, frequently almost globular ; sides 

 and front rounded ; beak of ventral valve small, much incurved over, and almost touching 

 the umbone of opposite valve, perforated at its extremity by a small circular foramen ; 

 the deltidium being completely concealed ; beak-ridges strongly marked. Dorsal 

 valve often gibbous, mesial fold rounded, and at times considerably elevated, especially 

 near the front. Ventral valve convex, divided by a deep sinus ; front raised into a 

 rounded wave. Surface of valves ornamented with numerous angular, branching, or 

 bifurcating ribs, more or less clustered together, so as to give to the surface an undulating 

 appearance. The valves are also crossed by many projecting undulating laminae 

 of growth, which overlap each other to a considerable extent. Interiorly two broad 

 coiled lamellae are attached to the hinge-plate, with vertical spires, closely adpressed, and 

 directed towards the disk of the valve. Two specimens measured — 

 Length 8, width 8, depth 6 lines. 

 „ 10, „ 11, „ 8 „ 



Obs. In the preceding description are given details in connection with this species 



