MUSEUM OF COMPARATIVE ZOOLOGY. 33 
the ornamentation of the surface cannot be determined from the specimens at 
hand. Mr. Billings describes them as being finely striated, “the strie curving 
forwards on the dorsal side, then passing upwards on the sides at nearly a right 
angle, curve slightly backwards on the ventrum.” The specimen described 
here is 11 mm. long, and is one of the smaller specimens of the species. 
Locality and position. — Station No. 2, North Attleborough, Mass., Cam- 
brian, one specimen. It occurs also at Troy, N. Y., and at Bic and St. 
Simon in Canada. 
14. Hyolithes princeps, Billings. 
Plate II. Fig 25. 
Shell large, straight, gradually tapering, very thin. The shells occur in 
large numbers throughout the section at Locality No. 1. Their outline is 
readily seen on almost any fracture of the rock in the bed in which the species 
is found; but owing to the irregular fracture of the rock and the large size of 
the species, as well as to the very frail nature of the shell, entire specimens 
are not found. The following description is drawn up from abundant frag- 
mentary material. 
The shells vary greatly in size, reaching at maturity a diameter of 9 or even 
11 mm. and a length of 100mm. or more. The dorsal side is flattened or mod- 
erately convex. The ventral side is decidedly convex; usually the convex- 
ity is more marked on one side of the ventral surface than on the other, the 
latter side being often almost flat. The median line is rounded, yet usually 
distinct enough to be recognized. The apical angle is very moderate. In some 
Specimens it is as low as 6°. In the original description of the species, it is 
said to be as high as 15°. The lateral angles are also more rounded than in 
typical specimens. The surface is marked by fine transverse striz. 
It will be noticed that the specimens here described do not closely accord 
with the type. The lateral angles are not prominent enough, and the apical 
angle is lower; but they agree with those forms in size and in general appear- 
ance. At any rate, the amount of variation seems insufficient to be ranked as 
specific. One interesting feature of these specimens is the frequency with 
which the shells of different individuals are found loosely inserted in each 
other so that three or four shells are successively sheathed one within the 
other, or they may be inserted side by side in a large individual. Small 
slender shells apparently belonging to Hyolithellus micans also occur in this 
position. Whatever may be the conditions of this sheathing, it does not 
suggest any structural connection between the different shells at the time of 
fossilization. 
Locality and position.— Station No. 1, North Attleborough, Mass., Cam- 
brian, 200 specimens. 
VOL. XVI. — NO. 2. 3 
