72 
PALAEONTOLOGY OF NEW YORK. 
the axis. The three pairs of lateral spines are curved regularly backward, 
while the four posterior spines appear to have been straight, and but slightly 
divergent. Within the margin, and just above the bases of the long third 
pair of spines, was another pair which, judging from the diameter of the 
broken base, must have had fully the length of the third pair. These spines 
were inclined at an angle of nearly forty-five degrees to the surface of the 
border. The actual length attained by all these spines is not indicated except 
for the third pair; judging, however, from their broken sections it is evident 
that they were of very considerable length. Across the posterior border the 
bases of the spines are continued as low ridges to the edge of the axis. 
Surface Ornamentation. The bulbiform termination of the axis is covered 
with closely set pustules of uniform size. The anterior furrow and the 
border are minutely granulose, and the surface of the spines is marked by 
elevated, frequently interrupted strim, which converge at an acute angle on 
the upper surface of the spine; towards the extremity of the spines these 
lines become stronger and much rounded, giving the surface a coarsely 
ridged appearance. 
Dimensions. The single specimen observed has a width across the anterior 
margin of 9 mm., a length of 8.5 mm. to the posterior margin, and of 33 mm. 
axially, as far as the apex of the third pair of spines. 
Observations. This extravagant form of Acidaspis is the only member of the 
genus as yet known in America from rocks younger than the Upper Helder- 
berg limestone. The great length of the caudal spines is equaled by no other 
known species of the genus and is approximated only by Acidaspis Dufresnoyi, 
Barrande."^ 
Distribution. Hamilton group. Little Traverse Bay, Michigan. 
* We are indebted to Dr. C. Rominger, of Ann A.i-bor, Michigan, for the discov'ery of this species, and 
through his favor the specimen has been made accessible for study and description. 
