1857.] THOMSON — ACIDASPIS. 207 



genis parum profundo sulco sejunctis ; cervice gibbo, retrorsum elon- 

 gato, bispinoso ; thorace segmentis novem, unispinosis ; capite pleu- 

 risque leviter granulosis, adspersis liic et illic tuberculis minutis ; cauda 

 brevi, transversa, semilunar! ; testa reticulata, margine quatuordecim 

 spinis radiantibus, aequalibus, ornata. 



Not above half an inch long. General form broad, rather square. 

 Head broad and short. Glabella triangular ; median lobe broad, 

 not very prominent. Two oral side-lobes entirel}^ circumscribed, 

 separated from the median lobe by distinct furrows. 



Portion of the cheek within the facial suture very gibbous. Ocu- 

 lar ridge distinct. Eyes somewhat remote. 



Neck-segment separated from the median lobe of the glabella by 

 a shallow groove ; gibbous, and continued backwards into two long, 

 diverging, straight or curved spines. 



Axis of thorax and abdomen narrow, prominent. 



Body-rings nine ; lateral portions horizontal, convex ; a longitu- 

 dinal furrow separates the convexity into two ridges, which coalesce 

 at the distal extremity, and end in a long, slightly recurved spine. 



Tail short, semicircular, of two short segments, fringed with from 

 twelve to fourteen long, radiating, equal spines ; a ridge from the 

 anterior axis-segment is continuous with the antepenultimate spine 

 on either side. 



General surface of the head and body-rings slightly tubercular ; 

 surface of tail reticulated. 



The form of the tail of this species at once distinguishes it from 

 all its British congeners, as indeed from all species hitherto described, 

 with the exception of A. radiata, Goldf., which it closely resembles. 

 The tail-spines of the present species are longer than in A. radiata 

 and slightly curved. The reticulation on the surface of the tail is 

 not brought out in the figures of ^. radiata. 



If Barrande's identification be correct, A. radiata must extend 

 upwards into the Devonians. A very slight distinction would, I 

 think, authorize us in denying so wide a range to a Lower Silurian 

 form. 



Locality. — Bather common in schists at the base of the " Graptolite 

 and Orthoceratite flags," Pinwhapple Glen, Ayrshire, = Upper Bala. 



AciDASPlS HYSTRIX, Sp. UOV. PI. VI. figS. 6-10. 



A. angusta, ovata, testa tuberculis minutis peromata; capite brevi, trans- 

 verso, glabella triangulari, lobo mediano longitudinali, utrinque duobus 

 lobis lateralibus, ovatis, a gena loboque mediano sejunctis; poste- 

 riori lobo laterali cervice gibbo coalescente ; thorace pleuris novem 

 bispinosis; cauda lata, brevi, spinis duodecim sequahbus, parallelis, 

 reflexis, fimbriata. 



Less than half an inch long. 



Glabella broadly triangular, not very highly arched ; middle lobe 

 rather narrow ; lateral lobes two, oval, separated by distinct grooves 

 from the central lobe and from the cheek ; hasal lateral lobe fused 

 with the neck-segment. Portion of cheek within the facial suture 

 very gibbous, likewise conjluent with the neck-segment. Neck- 



