138 The Ottawa Naturalist. [Feb. 



row into equally elevated portions. Silurian, Europe and 

 North America. 



Dicranurus, Conrad. Dorsal furrows weak on cephalon, 

 but the free and fixed cheeks not anchylosed. Occipital ring 

 with two very long spirally curved spines. Pygidium with only 

 a single pair of spines. Lower Devonian, Europe and North 

 America. 



Ancyropyge, Clarke. Margin of pygidium with 12 very 

 long slender curved spines. Devonian, North America. 



Selenopeltis , Hawle and Corda. Eyes half way to the front 

 of the cephalon. The pleural lobe of each thoracic segment is 

 crossed diagonally by a ridge which is extended into a very 

 long spine. Pygidium with only a single pair of spines. Ordo- 

 vician, Bohemia. 



GlaphMrus , Raymond. Probably does not belong to the 

 Odontopleuridae. 



Note on Dicranurus. 



The Dicranurus monstrosus (Barrande) of Bohemia is ex- 

 ceedingly like our D. hamatus Conrad, of New York. The col- 

 lection in the Musetmi of Comparative Zoology contains many 

 fine specimens of the Bohemian form, including the originals 

 of figures 1-3, plate 15, of the supplement to volume 1 of the 

 "Silurian System." The original of figure 3 is an indeter- 

 minable fragment, but certainly has nothing to do with the 

 pygidium of this species. The pygidium was unknown to Bar- 

 rande, but our collection contains an example from Lochkow, 

 where the species seems to be rather common. It is of the 

 same type as that described by Barrande as Acidaspis spoliata 

 (Suppl. 1872, p. 82, pi. 14, fig. 46). The type of this latter 

 species is from Mnienian, Bohemia, and it also is in the Museum 

 of Comparative Zoology. The pygidium is short, triangular, 

 and there are two strong spines which arise from the upper 

 surface of the test, and not from the margin. The spines arise 

 in the same way in Selenopeltis, the spines in that genus being 

 of considerable length, but seldom preserved, even on excellent 

 specimens. It is interesting that the oldest genus (Selenopeltis), 

 and the youngest (Dicranurus) , of the Odontopleuridae, should 

 both have a pygidium with an aspinose margin, while the other 

 members of the family all have numerous spines on the pygidium. 



American Species. 



In the following list I have attempted to arrange the Ameri- 

 can species in accordance with the above definitions. It is not 



