236 
PALAEONTOLOGY OF NEW-YORK. 
lateral lobe ; pygidium composed of two or three articulations above, with a fourth and 
last which is very long, and abruptly narrowing towards the extremity ; lateral lobes with 
three articulations on each side, which are marked by a narrow groove for about one third 
of their length ; central lobe separated from the lateral lobe by a deep narrow groove. 
The specimens which we possess are too imperfect to give a complete description of the 
fossil. Two of these are from Carlisle (Pa.), being the same figured by Mr. Conrad as 
cited above. It is certainly quite distinct from Asaphus, and clearly referable to Platynotus, 
when compared with specimens from Lockport, which have the posterior part of the glabella 
much narrower proportionally, and the entire fossil is less convex. The Lockport species 
likewise differs in the anterior extension of the buckler, which is not shown in our speci¬ 
mens, or in those figured by Capt. Portlock. The articulations of the thorax differ in their 
character ; and the posterior extension of the middle lobe of the caudal shield is much 
narrower in the Trenton species, than in the other. This feature is shown in our figures, 
as well as in those of Portlock before referred to. 
Emmrich, in his description of Nuttainia, quotes JY. hibernica as the typical form, 
remarking that u a perfectly corresponding species occurs at Lockport in North America.” 
I have already remarked that the Lockport species is distinct from the one under con¬ 
sideration, as well as from the figures of Portlock ; and the specimen referred to must be 
either distinct, or not from Lockport. 
Fig. 1 a , b. Portions of the buckler and caudal shield of this species. 
Fig. 1 c. A fragment of the buckler, more compressed than the preceding. 
Fig. 1 d. A magnified portion of the crust, showing the pustules upon the surface. 
Fig. 1 e. This figure is from a plaster cast of a specimen, the original of which is in the cabinet of Mr. 
Carly of Cincinnati. The specimen is from the Blue limestone of Ohio, and is apparently 
identical with our species. The oculiform tubercles are well preserved, but their true cha¬ 
racter cannot be learned from a cast. 
Position and locality. This species, so far as known, is confined to the Trenton limestone, 
or rocks of the same period. The specimens 1 a, b , are from Carlisle (Pa.), where they 
are associated with other Trenton limestone fossils. Fig. 1 c is from Middleville (N. Y.). 
Fig. 1 e is from a corresponding position at Cincinnati (Ohio). 
It is an interesting fact, that species of this genus appear in three distinct positions in the 
Silurian strata ; the first in the Trenton limestone, the second in the Niagara group, and 
the third in the Delthyris shaly limestone, which we must regard as near the termination 
of the Silurian period. 
