178 BRITISH FOSSIL CRUSTACEA. 



In Lowry's Chart of the Genera of Fossil Crustacea designed by Mr. J. W. Salter 

 and myself, Mr. Salter has figured a head -shield of Hemiaspis under the name of 

 //. Salweyi. There can be no doubt that this form is identical with Limuloides tubercu- 

 latus of Salter. I consider his Limuloides speratus and L. optatus to represent but one 

 species, closely allied to H. limuloides. A portion of the head-shield of another form 

 distinct from the foregoing, from the Wenlock Shale, Dudley, completes the known 

 species of Hemiaspis. Formation and Locality. — Lower Ludlow ; Leintwardine. 



Species 2.— HEMIASPIS SPERATUS :— H. Woodw. PL XXX, figs. 5 and 7. 



Limuloides speratus, Salter, MS. 

 — optatus, Salter, MS. 



This species is represented by four head-shields only; body-segments are not known. 



It is no doubt closely related to H. limuloides already described, but the carapace is 



broader in proportion to its length, and the radiating lines or ridges which in that species 



take their rise around 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 

 costae 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 



Fig. 68. — Head-shield of Hemi- , , , -, ;1 , . , 



aspi. speratus, Salter, ms. latero-antenor border; the two most posterior costae curve up- 

 Nat. size. (Restored.) wards and outwards from the posterior border of the glabella to 



e. posi wn o e eye ^ e lateral margins of the shield, and are marked midway by a 



minute lenticular space which probably indicates the position of the eye (see Fig. 68, 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 Hemiaspis speratus : 

 Breadth. Length. 



15 lines 7| lines (PL XXX, fig. 7), Mus. Brit. 



10"2 " O ). ( >> » 5)> » 



13 „ 8£ „ (Woodcut, Fig. 68.) Mus. Pract. Geol. 



Formation and Locality. — This species is found in the Lower Ludlow Rock of Leint- 

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

 Museum, and in the Museum of Practical Geology, Jermyn Street. 



