Yol. 52.] SILURIAN SPECIES OF ACIDASPIS. 239 



ACIDASPIS DEFLEXA, Sp. nOV. (PI. VII. fig. 7.) 



This resembles A. coronata so much that a full description is 

 unnecessary, and it will be sufficient to draw attention to the chief 

 points of difference. 



Head as in A. coronata ; but the genal spines are more slender, 

 and their outer borders make a distinct angle with the external margin 

 of the cheek. 



The thorax consists of ten segments, as in A. coronata ; but the 

 pleural spines are somewhat more delicate. 



Tail rather large, broad. Axis small, with two rings defined 

 upon it ; from the anterior ring a rib curves back on each side, and 

 is produced beyond the margin of the tail as a long slender spine, 

 slightly inclined outwards. Between these two primary spines are 

 two shorter ones, and outside each primary is a rudimentary point. 



Horizon and Localities. — Wenlock Limestone : Dudley ; Walsall. 



Affinities. — This is one of the forms which are commonly called 

 A. crenata in England ; but it is quite a distinct species, and is much 

 more closely allied to A. coronata. From A. crenata it is distinguished 

 by the outline of the head, the strength of the genal spines, the 

 absence of crenation on the frontal border, etc. From A. coronata 

 it is separated by the characters of the genal spine and of the tail, 

 as described above. 



Acidaspis crenata, Emm. sp. (PL VII. figs. 1 <fc 2.) 



1845. Odontopleura crenata, Emmrich, Neues Jahrb. 1845, p. 44. 

 1845. Ceraurus crenatus, Loven, Ofv. kongl. Vet.-A.kad. 1845, p. 47, pi. i. 

 fig. 1. 



Body oval, broad in front, narrowing rapidly behind. 



Head sub-quadrate, about twice as broad as long, margin incurved 

 in front. The glabella narrows slightly towards the front ; basal and 

 second lobes rounded, nearly equal in size, almost completely cut off 

 from the central part of the glabella. The occipital ring bears a 

 small tubercle. Frontal border crenate. Facial suture in front of the 

 eye nearly parallel to the axis, behind the eye it cuts the posterior 

 margin. Eyes very prominent, placed far back, close to the neck 

 furrow and near to the glabella. Free cheeks granular ; margin 

 provided with short spines ; genal angle produced into a long slender 

 spine, which at its origin is curved outward. 



The thorax consists of nine segments, which after the first two or 

 three decrease in width towards the tail. Axis about as wide as the 

 pleurae. Pleurae nearly at right angles to the axial line ; each bears 

 a prominent ridge, which, except in the case of the first two segments, 

 is produced into a long, slender, backwardly-directed spine. 



The tail exists in two forms (each of which has been found 

 attached to a complete specimen): — (1) very small ; consists of two 

 segments, the anterior of which is produced backward into a long 

 spine on each side ; two very short spines between these primaries ; 

 (2) much broader, with a broad flat area around the axis ; primary 

 spines not so long, secondary spines larger. These two forms prob- 

 ably belong to different sexes. 



