1893. ] NEW YORK ACADEMY OF SCIENCES. 241 
we may, perhaps, consider that the structure of Triarihrus was 
that of all the Olenide, the family to which it belongs ; while 
many of the later trilobites would come nearer to Calymene 
and Ceraurus in their structure. 
As regards the probable affinities of the trilobite as modified 
by Mr. Valiant’s discovery, the writer can scarcely venture any 
remarks, except tentatively. The homology with Limulus seems 
not to be as close in TVriarthrus as in the forms studied by Mr. 
Walcott ; but the characters seem to be of a more comprehen- 
sive type, approaching the general structure of the other crus- 
tacea rather than that of any special form. The presence of 
antennée need not, one would think, separate them from the 
rest of the Pcecilopoda, for a small pair occurs in Hurupterus,. 
and the anterior pair of appendages in Limulus are also thought 
to be modified antenne. The cephalic organs are peculiasy, if 
proved to be gills, and though in the solitary specimen showing, 
them they seem to belong to the head, yet further proof would 
be desirable, that they are not displaced, thoracic limbs, The 
fused pygidial flap would be a less important character, as it 
might easily be induced by change of conditions of life. 
As regards the habits of Triarthrus, we may conjecture that 
it usually scuttled through the soft mud which composed the 
shale in which it is found, on the little poimted walking legs ; 
but that it had considerable swimming powers, more, perhaps, 
than the later types of trilobites. 
It is hardly to be expected that these antenne, still less the 
other organs, will be found in specimens of trilobites unless: 
they be exceptionally well preserved; but one character, the 
arching of the anterior rim at the centre of the head—if not a 
mere accident of preservation in these specimens—may be found 
to exist in less perfect fossils, and would be a fair indication of 
the former existence of the antennz which passed under it, 
In conclusion, I wish to acknowledge the kindness of Prof. 
Kemp in allowing me the honor of describing these specimens. 
I have also to thank Prof, Whitfield for advice and assistance. 
in the subject, which has been very useful to me. 
[NorE.—As regards the supposed gills under the head, it would seem 
more probable that they were long, thickly set hairs or fimbrise on a nar- 
row limb, and served as mquth organs rather than gills, though, perhaps, 
also assisting in the respiration.—June, 1893. 
Transactions N. Y. Acad. Sci. Vol. XII. July 22, 1893. 
