﻿104 



SILURIAN TRILOBITES. 



Homalonotm is — Elongate, convex, with steep sides and a very broad axis, scarcely 

 distinguished from the pleurae. There are thirteen body-rings, deeply grooved, and the 

 fulcrum is close to the axis in most of the species. The head with an obscure quadrate 

 glabella, slightly lobed ; a rostral shield; and a quadrate labrum, tuberculate and gibbous in 

 the middle, and with a bilobed tip. Surface of the body scabrous, occasionally spinous. 

 Internally the cheeks have at their base a broad flat space next the glabella. 



Range. — Upper Silurian, and Lower (and Middle?) Devonian. 



The genus has not yet been satisfactorily divided, but the species may be conveniently 

 arranged in five, or possibly six, groups or subgenera, as follows : 



1. Brongniartia, Salter, 1865. Depressed, with broad rounded head, remote eyes, 

 well-defined lobeless urceolate glabella, and many-ribbed rounded tail. Lower 

 Silurian. 



§ 1. Body scarcely trilobed ; the axis broad. {H. bisulcatus is the type of the 

 subgenus, and of this section.) Lower Silurian. 



H. bisulcatus, Salter. 

 H. Sedgwickii, id. 

 H. Edgelli, id. 

 H. pfatypleurus, Green. 



§ 2. Body strongly trilobed ; the axis narrow. (Type, H. rudis ; this leads off 

 directly towards Calymene.) Lower Silurian. 



H. rudis, Salter. 



H. Bohemicus, Barr. 



H. varus, Corda. 



H. brevicaudatus Deslongch. 



H. Vicaryi, Salter. 



2. Trimerus, Green, 1832. Elongate, convex, with triangular head; eyes not remote; 

 a defined, but obscurely lobed, broad glabella. Thorax slightly lobed ; tail many-ribbed, 

 pointed, often acuminate. (Type, delphinocephahs.) Upper Silurian. 



H. delphinocephalus, Green. 

 H. Johannis, Salter. 

 H. cylindricus, id. 



3. Kcenigia, Salter, 1865. Convex; head wide transverse, with concave and tricus- 

 pidate front. Glabella subquadrate, well defined. Eyes rather approximate, on gibbous 

 cheeks. Tail pointed, many-ribbed. (Type, H. Knightii.) Upper Silurian. 



H. Knightii, Murch. 

 ? H. ludensis, Salter. 



