578 The American Naturalist. [June, 
the lower sectorial has been shown to be an inconstant character in the 
genus. In this specimen it is well developed. 
MEASUREMENTS D. bombifrons D. felina 
M M 
Length of skull, condyles to premaxillaries, .185 .154 
Length of skull including overhanging 
occiput, .205 
Length of cranium to anterior rim of 
orbit, .130 .108 
Length of face, .055 .046 
Distance from anterior rim of orbit to post- 
orbital constriction, .065 .050 
Length of bony palate, i .074 .072 
Breadth of bony palate, posterior portion, .070 .069 
Breadth between canines, .025 .026 
Distance from foramen magnum to line of 
post-glenoid process, .039 .033 
Distance from foramen magnum to line of 
mastoid processes, 0195 0195 
Length of upper molar series, 046 .049 
Length of upper canine, .050 
Upper canine, transverse diameter, »» SOO .008 
‘Upper canine, fore and aft diameter, 019 .012 
Length of mandible from condyle, .132 119 
Length of lower molar series, 055 .052 
Lower canine, transverse diameter, 007 006 
Lower canine, fore and aft diameter, 110 008 
Geo. I. ADAMS. 
Geological News, Parrozorc.—Mr. Beecher’s study of a series 
of Trinucleus concentrieus Eaton, a trilobite departing widely from the 
common form, substantiates the conclusions of Barrande as to the 
generic value of the ocular tubercle and eye-line. They clearly repre- 
sent adolescent characters. 
In regard to the appendages of T. concentricus, Professors Verrill 
and Smith agree that they indicate an animal of burrowing habit, 
which probably lived in the mud of the sea-bottom, after the fashion of 
the modern Limulus. In addition to its limuloid form, the absence of 
eyes favors this assumption, so does the fact that many specimens have 
been found preserving the cast of the alimentary canal, showing that 
