Inner organs, such as the heart and stomach, might have been attached to the shell along impressions a and b. Also along or behind c and h, which both continue into the free cheeks, ligaments or muscular fibers may have been inserted. From d, e, f, and g, muscles have very likely gone out to the cephalic appendages. Against this it may be urged that impression d is too far forward to have belonged to the first pair of feet. Again, the impression h may in reality represent two confluent muscular insertions, from the first of which, in that case, arose the muscles of the fourth pair of cephalic feet. Were this the case, the muscles of the first pair of cheek feet should be attached at e. And d in turn may be explained as the attachment of the muscles of the antennæ, k those of the hypostoma, and from i possibly those of the epistoma. That k is here named as the starting point of the hypostomial muscles and not those of the antennæ, depends partly on the analogous position of i and partly on the fact that the hypostoma of _Nileus armadillo_ (text figure, in which the outline of the hypostoma is dotted), by reason of it? wing-like border, could not have permitted the antennæ to reach forward, but rather only outward or backward. My own explanation would be that impressions e, f, and g correspond to the glabellar furrows, h the neck furrow, and all four show the places of attachment of the appendifers. Those at d may possibly be connected with the antennæ, although I should expect those organs to be attached under the dorsal furrows at the sides of the hypostoma. It will be noted that either b, k, or i correspond well with the maculæ of the hypostoma and some or all of them may be the points of attachment of hypostomial muscles. They correspond also with the anterior scars of _Dalmanites_. EYES. While I have nothing to add to what has been written about the eyes of trilobites, this sketch of the anatomy would be incomplete without some reference to the little which has been done on the structure of these organs. Quenstedt (1837, p. 339) appears to have been the first to compare the eyes of trilobites with those of other Crustacea. Johannes Müller had pointed out in 1829 (Meckel's Archiv) that two kinds of eyes were found in the latter group, compound eyes with a smooth cornea, and compound eyes with a facetted coat. Quenstedt cited _Trilobites esmarkii_ Schlotheim (=_Illænus crassicauda_ Dalman) as an example of the first group, and _Calymene macrophthalma_ Brongniart (=_Phacops latifrons_ Bronn) for the second. Misreading the somewhat careless style of Quenstedt, Barrande (1852, p. 133) reverses these, one of the few slips to be found in the voluminous writings of that remarkable savant.