482 GEOLOGICAL SURVEY OF THE TERRITORIES. 



genus; liis species sinmilosusy uot only being his first one, but the only 

 one that he refers to his new genus, without a mark of doubt. On the 

 other hand, the question is complicated by the fact that his typical spe- 

 cies is founded on a separate head, divested of the movable cheeks, and 

 the detached pygidium allnded to above, which njay, or may not, belong 

 to the sanui species or genus as the head ; while in the text, he places a 

 mark of doubt after the reference to the figure 11 of the pygidium, thus 

 showing, as one would think, that he only refers it doubtfully to the 

 species spimdo.sua. Yet, it is evident that the name spinulosus was 

 suggested for his first species by this pygidium, which is armed with 

 small tspines, while no spines are known to be connected with the head. 

 But another difficulty arises from the fact that his ^e«enc name Corynex- 

 ochus seems to have been suggested by the prominent clavate char- 

 acter of the glabella of the head figured by him. 



For this latter reason, and the fact that the pygidium is only con- 

 nected by him doubtfully with the head, probably most authorities 

 would view the species to which the head belongs (in case the pygidium 

 appertains to another form) as type of tlie genus. If we adopt this 

 view, it woidd be somewhat doubtful whether our species could be prop- 

 erly referred to Angelin's genus, since its glabella is merely cylindrical, 

 and uot quite as long as the head, instead of widening out anteriorly to 

 nearly twice its ])Osterior breadth, and apparently slightly overhanging 

 the anterior margin, as in the head figured by Angeliu. 



If the difference in the form of the glabella mentioned above should 

 not be of generic importance, and there should be no well-defined ditt'er- 

 ences in the abdominal parts of Angelin's type, (the abdomen of which 

 is unknown,) then our species would have to be referred to the same 

 group, and take the name CorynexocMis serratus. It is, however, also 

 very closely allied to Bathyurus, Billings, in most of its known charac- 

 ters. After examining casts of our species, Mr. Billings writes that he 

 would uot be willing to separate it generically from B. extans, the type 

 of his genus ; though he admits that some difi'ereuces in the abdominal 

 parts, to which I had called his attention, are rather marked. These 

 are the presence of only seven body-segments in our type, instead of 

 nine, as in B. extans, and the other known species of Bathyurus ; while 

 the plnral furrows in our species are very broad aud rounded, instead 

 of narrow and sharply cut as in typical Bathyurus. The serrated, or 

 spinuliferous character of the pygidium, in the form under considera- 

 tion, is another difference, though probably of less importance. Mr. 

 Billings, however, writes that he has several new species (all from the 

 Lower Potsdam) showing this character; which fact would seem to 

 argue that there may be a group characterized in part by this pecu 

 liarity. 



From all the facts, I should certainly be disposed to separate our 

 type at least sub-generically from Bathyurus^ were it not for the doubts 

 that still remain iu regard to its relations to Corynexochvs of Angelin, 

 which, I should have remarked, would have to take precedence over 

 Bathyurus, if founded on a congeneric type, because it was published iu 

 1854, and Bathyurus in 1859. 



Locality and position. — East side of Gallatin River, above Gallatin 

 City, Montana Territory. Potsdam Group of tbe primordial zone. 



Bathyurus ? Haydeni, Meek. 



General form oval, rather depressed; outline of cephalic shield un- 

 known. Glabella narrow subcyliudrical, most convex near the middle, 



