HEMIASPIS LIMULOIDES. 175 



Since that date other fragments have been obtained, and also another nearly perfect 

 example (obtained by the late Mr. Henry Wyatt-Edgell) of the species named by me 

 Hemiaspis limuloides, which, having the upper central portion of the carapace preserved, 

 nearly completes our knowledge of this species. 



The great interest attaching to this form arises from the fact that it offers just the 

 desiderated link by which to connect the Xiphosura with the Eurypterida. 



Idmuli, apparently differing but little as regards their carapace from the recent species 

 now found living on the Coasts of China, Japan, and the north-east coast of North 

 America, occur as early as the deposition of the Solenhofen Limestone of Bavaria ; and 

 in the Coal-measures of England and Ireland several species of Bettinuri and Prestwichia 

 occur, in which the cephalic shield is composed of the cephalothorax ; and the segments 

 of the abdomen, if not anchylosed in all, are so in most. 



But in the specimen under consideration we have the cephalic, thoracic, and 

 abdominal divisions still remaining distinct, and apparently capable of separate flexure. 

 This important character at once separates it from Limulus, Bettinurus, and Prestwichia. 



I did not on this account {icith the concurrence of Mr. Salter given at the time) 

 use his MS. name of Limuloides as a generic appellation, but proposed the name 

 Hemiaspis (from rj/uiavc, half, and a<77nc, a shield), reserving Mr. Salter's MS. name Limuloides 

 for the specific title of the most perfect species of the genus (see PL XXX, figs. 1,2). 



But it will be observed that Hemiaspis is also, in general appearance, strongly severed 

 from the other species of Eurypterida, as well as from the Xiphosura, in structure. 



The three divisions into head, thorax, and abdomen are more strongly marked. The 

 abdomen is reduced to very slender proportions, less than one third the length of the 

 animal (the entire specimen measuring 2^ inches in length by one inch in width. 



The carapace in general outline resembles Limulus, but is more dilated laterally. 

 There is a small stellate ornamentation in the centre of each cheek, having five to six rays, 

 and measuring about a line in extent ; but whether this represents the position of the 

 eyes I am quite unable to say. It is so unlike the eye of any other member of the group, 

 that I am inclined to doubt its relation to that organ. It seems probable that the eyes 

 were placed along the lateral margin of the glabella, not upon the centre of the cheek. 



There is a faint indication on one side of fig. 1 and on fig. 2 of a facial suture to the 

 head-shield (as in the Trilobites), with a small aperture upon its border, which may 

 possibly indicate the true position of the eye, but it is by no means clearly defined. 



The surface of the glabella when perfect (as shown in our Plate XXX, fig. 2) appears 

 to have been almost smooth, 1 save that it is traversed by two ridges which, commencing 



1 In the original description of the glabella of Hemiaspis limuloides (see ' Quart. Journ. Geol. Soc.,' 

 vol. xxi, p. 490) I have described the glabella, from a detached portion, as " ornamented with a semicircle of 

 nine tubercles, and a tenth immediately within the circle upon the elevated front, and two small tubercles at 

 the posterior margin." The acquisition of the second specimen (fig. 2, pi. xxx) proves this fragment to 

 belong to another species, not to H. limuloides, as formerly supposed. 



