EURYCARE. 93 



and thorax of L. salteri,he says, are very similar to those of Angelin's Leptoplastus, 

 " the tail, however, is quite different from that genus, being broader than long, 

 emarginate behind, and entire, as against triangular and toothed." It seems 

 doubtful, however, whether these differences can be considered of subgeneric 

 rank. In L. ovatus and L. raphidophorus the tail is triangular and toothed, but in 

 the type-species of the genus, which is L. stenotus, the tail is broader than long 

 and is not triangular, and the teeth are so minute that they are usually 

 indistinguishable. 



Raw's observations, however, certainly suggest that the triangular toothed tail, 

 like that of L. ovatus, represents an early stage in the evolution of the genus. 

 According to him, young specimens of L. saltevi show this character, while in 

 later stages the tail becomes broader and loses its teeth. 



Horizon and Locality. — Shineton Shales : Shineton. 



Genus EURYCARE, Angelin. 



As a rule Eurycare is easily distinguished from Sphaerophthalmus and Lepto- 

 plastus by the great width of the head, the length of the genal spines, the remote 

 position of the eyes, and the narrowness of the thoracic axis. Moreover, the 

 number of thoracic segments is 12 — 1 7, while in Sphserophthalmus it is 7—9, and in 

 Leptoplastus 11 — 12. It is not always easy, however, to separate Eurycare from 

 Gtenopyge. In Eurycare the pleurae end in short points; in Ctenopyge the pleurae 

 of the posterior segments terminate in long geniculate spines, but those of the 

 anterior segments often end in points. The tail of Ctenopyge pecten is certainly 

 very different from that of Eurycare, but, as already noted (p. 79), it is by no 

 means clear that all the species referred to Gtenopyge possess tails of this type. 

 It is, however, when only the head is found that the greatest difficulty arises. In 

 both genera the head is very wide in proportion to its length, and the eyes are 

 more or less remote from the glabella. On the whole, these characters are most 

 strongly marked in Eurycare, but in some species, such as E. angustatum, Ang., 

 this is not the case. In Eurycare the glabella is usually shorter in proportion to 

 its length than in Ctenopyge, and perhaps rather less rounded in front. In 

 Eurycare, in fact, the glabella approximates more nearly to a square, while in 

 Ctenopyge it is more cylindrical, tapering slightly forwards ; but the difference 

 is not very strongly marked in all species, and when only the cranidium is 

 available it is not always possible to decide the genus with certainty. 



The more important characters of the genus may be summarised as follows : 



Head short, broad, with long genal spines springing abruptly from the external 



margin ; glabella short and more or less square in outline ; eyes small, about 



half-way between the anterior and posterior margins, remote from the glabella, 



with a long ocular ridge running towards the anterior angles of the glabella. 



