320 Silurian Fossils. 



as to form an easily recognized net-work upon the surface of the 

 rock. The edges of the plates contain the numerous cell cavities 

 of the polyps. These are small, oval, and varying in size from one 

 half a line to one line in length. 



Halysites is from the Greek halysion^ a small chain or necklace, 

 and lithos, a stone ; catenulatuSj Latin, from catena, a chain, or 

 catella, a small* chain ; catenojpora, from the Latin catena, a chain, 

 and the Greek pora, a pore ; escharoides, from the Greek, eschara, 

 a gridiron. 



Homolonotus delphinocepkalus. 



This trilobite has thirteen segments in the thorax and in the 

 caudal shield or tail, eleven to thirteen in the central lobe, and 

 from seven to nine in each of the lateral lobes. The head 

 is ovate or sub-triangular; the tail is also sub-triangular and 

 pointed at the extremity; each one of the articulations of the body 

 has a groove running nearly its whole length near the front 

 margin. The surface is rough and granulated. This is one of 

 those species trilobites the central lobe of whose body is scarcely 

 definable, the articulations being without the sharp bend on each 

 side the centre, which constitutes the middle lobe in many other 

 species. The glabella, or that portion in the centre of the head 

 which is usually elevated in the trilobite, has in this species very 

 little if any prominence. The eyes are small. The facial suture, 

 as described by Professor Hall, is parallel and coincident with, or 

 slighty within, the flexure of the margin (in front,) passing thence 

 obliquely through the eye, and turning comes to the margin a 

 little above the posterior angle. It abounds in the Niagara for- 

 mation and also in the Wenlock limestone in England. 



