SECTION IV., 1911. [111] Trans. R.S. C. 
Notes on Parallelism among the Asaphide.* 
By Percy E. Raymonp, Pu.D. 
Presented by Lawrence M. Lampe, F.G.S. 
And read May 17, 1911 
Isotelus gigas is probably the most common trilobite in the Ordo- 
vician rocks of Canada and the United States, and yet it is one of the 
species of which little is known. It is the custom to group all the smooth 
asaphids of the Ordovician under this name, but it will probably be 
found that not more than one half the specimens so labeled belong to 
this species, and probably one quarter of them belong to other genera 
than Jsotelus. These trilobites are not easily identified, and the at- 
tempt to separate the different forms has led the writer to a study 
of the family. This study has brought together a quantity of data 
bearing upon the relationships of the various groups. 
I am not yet prepared to give a formal definition of the family Asa- 
phide, but they may be briefly characterized as opisthoparian trilobites 
with large head and abdomen shields, prominent eyes, eight segments 
in the thorax, and always with a median vertical suture in the doublure 
of the cephalon. The family as thus defined, is less extensive than as 
defined by Beecher in the American translation of Zittel’s Paleontology, 
and contains 27 genera or subgenera, which are enumerated below. 
Ontogeny. 
Unfortunately, very little is known of the ontogeny of any member 
of the Asaphide. The nepionic stages of Asaphellus have been described 
by Matthew, but the series of stages even in this genus is very incom- 
plete. Scattered notes on the ontogeny of Jsotelus have been published 
by Clarke, Walcott, and Raymond and Narraway, while Salter pub- 
lished a few illustrations of immature specimens of Homalopteon and 
Ogygia corndensis. After a review of what has been published, par- 
ticularly the work of Matthew on Asaphellus, it seems that the following 
may be looked upon as primitive characters in this family.— 
1. Strongly segmented cephalon and pygidium. 
Absence of depressed borders. 
Long glabella. 
Eyes distant from the glabella. 
Facial suture marginal in front of the glabella. 
Pygidium and cephalon short and broad. 
Axial lobe narrow. 
Genal spines present. 
So Bl Cee We Gets 
*Published by permission of the Director of the Geological Survey. 
