90 INTRODUCTION. 



depressions do not occur in all the specimens ; they have been long known, and were 

 figured in Blainville's ' Malacologie.' 



Geol. range. — XJncites is at present known to occur only in the Devonian system, 

 and seems to characterise a certain horizon. 



Examples .- TJ. grypkus} Sch. sp. ? ; Icevis, M'Coy.'' 



Genus — A.iKxvk, Dahnan, 1S27. 

 Type — A. reticularis, Linn., sp. Int. PI. VII, figs. 87 — 94. 



Anomia (part), of Linnceus. 

 Tekebratulites (part), oi Schloth. 

 Terebratula, of the generality of Authors. 

 Atrypa, o{ Dalman, (part), Kin(/ and Smo. 

 Spirigerina, D'Orb., 1847, M'Coy. 

 Terebratula CALCispiRiE, Quenstedt. 

 HiPPARiONYX (part), Vanuxem. 



Animal unknown. Shell circular, transverse or elongated, furnished with mternal 

 spires, valves articulating by teeth and sockets ; beak produced or incurved, and slightly 

 truncated by a small round opening separated or not from the hinge-line by means of a 

 deltidium; false area at times well defined, dental valve convex, or almost flat, with a 

 longitudinal depression or sinus ; socket valve convex, with or without a mesial fold ; 

 surface smooth, striated or variously costated and imbricated by squamose lines of growth, 

 often considerably produced beyond the margin, under the shape of tubular spines or 

 foliaceous expansions ; structure fibrous and impunctate ; spiral appendages originating at 

 the base of the socket walls, and forming two large hollow cones placed horizontally, with 

 their apices directed inwards and towards the hollow of the same valve, which they almost 

 fill ; the inner sides of the spires are pressed together and flattened, with their terminations 

 close to each other near the centre of the bottom of the shell. In the interior of the 

 socket valve, the quadruple impressions of the adductor muscle are separated by a medio- 

 longitudinal ridge ; the pedicle muscles were probably affixed to the two small cardinal 

 plates. In the dental valve at the base of the teeth a semicircular ridge curves on each 

 side, forming a saucer-shaped depression open in front, and into which were implanted the 

 shell and pedicle muscles; the cardinal muscles seem to occupy the largest portion of the 

 depression, and to have been divided by an obscure mesial ridge; beyond these and a 

 little higher up are placed the pedicle muscular impressions, and above the mesial ridge, 

 nearer the beak, is seen the oval scar left by the adductor. 



' This species was figured and described by Beuth, &s. a Terebratula, in a work entitled 'Juliseet 

 Montium Subterranea,' &c., p. 134, No. 74, 1776. Professor Quenstedt likewise partly describes and 

 figures the genus in his ' Handbuch der Petrefackunde,' 18.51, pi. xxxvi, fig. 40, a, b, c. 



2 British Pal. Fossils of the Camb. Mus., pi. ii, a, fig. 6, 1852. 



