H. Woodivard — Notes on Palceozoic Crustacea. 437 



Fig. 5. — Head-shield of Semiaspis 

 speratus, Salter, MS. Nat. size. 

 (Restored.) e, probable position of 

 the eye. 



the margin of a well-defined central glabella, in H. speratus extend 



over the whole surface, save a small 

 quadrate area at the centre of the 

 posterior border. From this small 

 area seven diverging costse are given 

 off: the three in front being nearly- 

 equidistant and straight, the two next, 

 which rise from the outer angles of the 

 central area, divide and form a Y- 

 shaped ridge on each latero-anterior 

 border ; the two most posterior costae 

 curve upwards and outwards from the 

 posterior border of the glabella to the lateral margins of the shield, 

 and are marked midway by a minute lenticular space, which prob- 

 ably indicates the position of the eye (see Woodcut, Fig. 5, e). 



The head-shield is broadly-arcuate in front, and the margin, 

 especially on the cheeks, is fringed with a closely set row of minute 

 spines ; the lateral angles of the shield are truncated, not produced 

 posteriorly ; the hinder border of the head-shield is armed with four 

 equidistant spines. The surface of the carapace, especially around 

 the border, is covered with a very minute granular ornamentation. 

 The following measurements show the relative size of the head- 

 shields of Semiaspis speratus : 



Breadth. Length. 



15 lines 74 lines (Plate X. Tig. 7), Mus. Brit. 



101 „ 6 „ ( „ Fig. 5) 



13 „ 9 5j Mus. Pract. Geol. 



1^ ), " )» i> >) 



This species is found in the Lower Ludlow Eock of Leintwardine, 

 and is represented by specimens of the head only, preserved in the 

 British Museum, and in the Museum of Practical Geology, Jermyn 

 Street. 



Species 3. — Hemiaspis Jiorricliis, H. Woodw., Plate X. Fig. 6. 

 This sjDecies, represented by a single example obtained by Charles 

 Ketley, Esq., from the Tunnel shale, Dudley, and now preserved in 

 the British Museum, is the oldest example in time of this curious 

 genus. 



When entire the carapace must have measured IJ inch in breadth 

 by 8 lines in length ; the edge is thickly set with prominent sharp- 

 pointed spines ^ a line to a line in 

 length, whilst two strong spines, 2 

 lines in length, project from each 

 posterior angle of the carapace ; the 

 spines along the hinder border of the 

 shield, if present in tliis species, are 

 not preserved in this example. The 

 median line of the carapace, which 

 is slightly tumid, is marked by one 

 rounded and prominent tubercle and 

 two elongated confluent ones, whilst 

 on either side of this median line three other divergent lines of 





n 



Fio. 6. — Head-shield of Hemiaspis 

 horridus, H. Woodward. (Restored.) 

 Wenlock shale Tunnel, Dudley. 



