AND DISTRIBUTION OF TRILOBITES. 273 
VI. Ilenus, Dalm. emend. Without glabella and without ar- 
ticulation of the tail. Body (9) 10-jointed. Joints smooth. 
Kyes distant from the axis of the head, situated nearer to 
the margin.—Silurian. 
Besides the already known species, viz. I. crassicauda and cen- 
trotus, I consider Bumastus Barriensis, Murch., as belonging 
here. 
B. Ogygie. Not contractile. Caudal shield large, articulated, 
generally very much flattened. Glabella clavate. 
VII. Ogygia, Brong. emend. Body 7 (?) 8-jointed. 
O. Guettardi, Brong., Desmarestii, Brong., Buchii, 
Brong., dilatata, Brinn (Pl. IV. fig. 9.). Characteristic for 
the lower Silurian strata. 
Asaphus tyrannus, Murch., does not belong here (to which 
division I have referred it in my ‘ Dissertation ’), but to Asaphus. 
VIII. Brontes, Goldf. Caudal shield clypeoid, with radiating 
ribs. Body 10-jointed. 
Br. flabellifer, Goldf., &c. Characteristic for the Devo- 
nian rocks. 
IX. Nuttainia, Eaton, Portl. Fins of the caudal shield distinct, 
connected only by their margins, terminating in triangular 
points. Body 10-jointed. 
N. hibernica, Portl. (Pl. IV. fig. 8.).—Ireland. A perfectly 
corresponding species occurs at Lockport in North America. 
Family III. Calymene.—Generally with “ oculi hiantes,” 
smooth horny membrane seldom preserved, reniform, not seated 
on conical protuberances. Facial suture extending to the co- 
vering of the cephalic shield. Glabella distinct, generally nar- 
rower towards the anterior portion. Body 12-jointed and upwards. 
Joints furrowed. Caudal shield articulated. Ellipsocephalus 
alone forms an exception. 
A. Genuine Calymene. Possessing the power of contraction. 
X. Encrinurus, nov. gen. ovpa, the tail, and Encrinites. Eyes 
smooth. Glabella clavate. Caudal shield furnished with 
a many-jointed axis and few fins. 
Entomostracites punctatus, Wahlenb., differs so much from all 
other Trilobites, that it well deserves to form a particular genus ; 
it unites the clavate forehead of the Asaphi with the course of 
the facial suture and shape of the eyes of Calymene. It forms 
