358 PALEONTOLOGY OF THE EUREKA DISTRICT. 
that the eyes in the smaller individual are a little distant from the glabella and 
united to it by a very short ocular ridge; otherwise no embryonic features 
are indicated. The example of the head of O. Iddingsi is still smaller, but 
it does not present any recognized embryonic features. 
Olenellus Gilberti and O. Howelli also occur at the same relative geologic 
horizon, at Pioche, Nevada, 130 miles (209.2 kilometers) distant. The for- 
mer species in that locality is noticeable in having, in the smaller specimens 
observed, an obtuse angle in the posterior margin of the head midway 
between the genal angle and the glabella (see outline, fig. 14, plate xxi). In 
the larger specimens the angle is near the outer portion of the margin or a 
little within the postero-lateral angle. The facial suture back of the eye 
is quite unlike that of O. Howelli, as shown for the latter in figs. 5 and 6, 
and cuts the posterior margin between the angle, 2 x, of the margin and 
the glabella, as seen in figs. 14 and 17. In comparing with O. Thompsoni and 
O Vermontana Hall, from the Georgia slates of Vermont, it is only to be 
observed that in the former species the general features of the adult, as far 
as known, appear to be the same, and that in the latter the facial suture has 
the same course back of the eye as in O. Gilberti, and Prof. R. P. Whitfield 
has shown me a‘ specimen in the collection of the American Museum of 
Natural History that is marked by a very short spine on the obtuse, rounded 
angle of the posterior margin, a short distance within the postero-lateral 
angle, a character not observed in any other species of the genus. 
Mention has been made of Olenellus asaphoides and certain resemblances 
in the contour of its head at the stage of development represented by fig. 11, 
and that of the head of O. Howelli as seen in figs. 1, 3, 5, ete. The curious 
interocular spines of the former have not been seen in O. Howelli. Mr. Ford 
has called attention to the Paradoxides-like run of the posterior margin of 
the head, g a, wg, fig. 11, and states that it disappears altogether during the 
embryonic life of that species. We have shown that it is extravagantly 
developed in O. Howelli, even to the extent of changing the entire contour 
of the head, fig. 2, and that it persists in the adult stage of many individuals 
of this species, and is also present in O.. Gilberti and O. Vermontana. 
In all the observed specimens of O. Howelli showing the facial suture 
back of the eye the posterior margin is cut by it at the angle within the 
