244 
PALAEONTOLOGY OF NEW-YORK. 
Fig. 1 g. The cephalic shield, represented in fig. 1 a; showing the separation of the maxillas y y at the 
facial sutures. 
Fig. 1 h. The right maxilla, separated* from the cephalic shield, as it appears in a fragment of the lime¬ 
stone. 
Much confusion in regard to this species exists in the works of foreign authors, several 
distinct forms being erroneously referred to the same ; while the real one, which doubtless 
occurs in several localities, is referred to another genus. Capt. Portlock, though disposed 
to recognize and identify all American species, has failed in this instance, and his Amphion 
gelatinosus can scarcely be any other than our species. This difficulty has arisen in part 
from the obscure specimen from which Green’s cast was made, the character of the buckler 
being very indistinct, though the nodulose articulations are well preserved. 
Emmrich, in his memoir, remarks that the Amphion gelatinosus of Portlock belongs to 
Phacops , a section of the Genus Calymene of Brongniart, having reticulated eyes. This is 
quite untrue, however; for the eyes of Ceraurus are peculiar, and quite different from 
those of Phacops , as they are from those of Calymene ; while the facial suture is similar in 
direction to the former, and the labrum, as in that genus, is attached by a suture to the 
front of the glabella. 
More recently, Dr. Loven ( id, cit .) has attempted to prove the identity of Ceraurus , 
Odontopleura and Acidaspis ; but he has misapprehended the characters of the Ceraurus., 
owing to the obscurity of the model of Green. I shall hereafter be able to show that the 
Ceraurus is restricted to the lower epoch of our palaeozoic strata, while Acidaspis ( Odonto¬ 
pleura ) is a genus continued into the lower and middle palaeozoic strata, and differing 
essentially from Ceraurus in many other particulars, as well as in the direction of the 
facial suture. 
I have given the numerous figures of this species, and of the parts usually found in the 
Trenton limestone, with a view of establishing the characters of the genus, and its clear 
distinction from other genera of Trilobites in the older strata. Notwithstanding all that is 
given, however, the entire characters of the species are not represented, as will be seen 
from the transverse view of a single articulation (PI. 65, fig. 1 n) , which is well preserved 
on the surface of a slab of limestone, showing the extended extremities, which bend 
abruptly downwards and curve slightly backwards, terminating in an obtuse point. 
Position and locality. This species, so far as known in New-York, is restricted to the 
period of the Trenton limestone. It is found at Middleville, Trenton falls, Lowville and 
Watertown, and is more rarely seen in localities in the Champlain valley. It is also known 
in several western localities and in Canada, showing a wide geographical range. The large 
fragment figured on Plate 66 is from near Cincinnati, Ohio. 
