508 ` Recent Literature, [July, 
Limulus and the Trilobites the corneal lenses appear usually to 
be round, and yet in making a camera drawing (as are 
p all those here represented) of the cornea of Limulus 
hen = from above, they present the same hexagonal appear- 
Lenses of ance as in the Trilobites. The cause of this I leave 
ferphus. to others to explain. 
In a section (transverse) of the cornea of Bathyurus longistrino- 
sus, received from Mr. Walcott, the lenses are seen to be very 
irregular, five or six-sided, and very irregularly grouped, not 
arranged in distinct rows. 
From the facts here presented it would seem evident that the 
hard parts of the eye of the Trilobites and of Limulus are, 
throughout, identical. The nature of the soft parts will, as a 
matter of course, always remain problematical; unless the dark 
line indicated in Fig. 3 (cl) really represents the outer edge of 
the pigment of the retina; but however this may be, judging by 
the identity in structure of the solid parts, we have, reasoning 
by analogy, good evidence that most probably the eye of the 
Trilobites had a retinal mass like that of Limulus, and that the 
numerous small branches of the long slender optic nerve (for such 
it must have been) impinged on the ends of the corneal lenses. 
It has been shown by Grenacher and myself that the eye of Lim- 
ulus is constructed on a totally different plan from that of other 
Arthropods; I now feel authorized in claiming that the trilobite’s 
eye was organized on the same plan as that of Limulus; and thus 
when we add the close resemblance in the larval forms, in the gen- 
eral anatomy of the body-segments, and the fact demonstrated by 
Mr. Walcott that the Trilobites had jointed round limbs (and 
probably membranous ones), we are led to believe that the two 
groups of Merostomata and Trilobites are subdivisions or orders 
of one and the same sub-class of Crustacea, for which we have 
previously proposed the term Paleocarida. 
:0: 
RECENT LITERATURE. 
Tue Geoocy or Wisconsin.\—This bulky report has not only 
a handsome typographical appearance, but is well illustrated by 
numerous excellent plates, and an atlas of maps. It bears every 
appearance of care and labor in its preparation, and of containing 
Geology of Wisconsin, Survey of 1873-1879. Vol. 111, Accompanied by an Ailas 
of Maps. J. C. Chamberlain, Chief Geologist. Madison, Wis., 8vo. pp. 763- 
