538 



CRUSTACEA. 



still more curious Deiphon, of the Silurian rocks, the fixed cheeks 

 are rudimentary, and are reduced to two curved spines, which spring 

 from the sides of the swollen glabella, and carry the faceted eyes, 

 while the free cheeks are obsolete. The axis of the tail is formed 

 of four or five rings, and the pleurae are prolonged into two spines 

 on each side, one of these being formed by the first segment only, 

 while the other, and much larger, one is made up of the amalgamated 

 extremities of the remaining segments. 



Family ii. Encrinurid^e. — This family is confined to the 

 Ordovician and Silurian periods, and is related to the preceding 

 through the intervention of Amfihion. The head is fairly devel- 



Fig. 397. — a, Head-shield of Encrinurus 

 punctatus — Silurian; b, Head-shield of 

 Croiiius intercostatits — Silurian ; c, Head- 

 shield of Cybele bcllatula — Ordovician. 

 (After Barrande.) 



Fig. 398. — a, Cybele Lo7>eni, of the 

 natural size ; B, Cast of the pygidium 

 of Cybele verrucosa, enlarged twice. 

 From the Ordovician rocks of Girvan. 

 (After R. Etheridge, jun., and the 

 Author.) 



oped, the genal angles rounded or pointed, and the facial sutures 

 discontinuous, and cutting the outer angles of the cephalic buckler. 

 Eyes are present, though not of large size, and the glabella may 

 or may not exhibit distinct lateral grooves. The surface is tuber- 

 culated, and some or all of the body-rings may bear spines. The 

 thorax generally consists of eleven segments ; and the tail, though 

 moderate in size, has a well-marked axis, which is composed of 

 very numerous rings. 



In Encrinurus (fig. 397, a) the glabella is pyriform, strongly 

 tuberculated, with the lateral furrows almost obsolete. The body- 

 rings are eleven in number, and the axis of the pygidium is com- 

 posed of extremely numerous rings. In this genus, as in its near 



