close relationship existing between S. excelsior and S. cestrotus is also indicated by the presence of paired spinous appendages on the first pair of legs of the former which correspond to those on the second and third pairs of legs in S. cestrotus. We have above proposed the subgenus Ctenopterus for this well defined group of species.
Another alteration of the restoration of S. excelsior, suggested by evidence afforded by S. cestrotus, relates to the structure of the eyes. The carapace of Beecher's restoration is a cast from the Rutgers College specimen. In this the eye regions 
Figure 66 The terminal portion of the median dorsal ridge of Stylonurus excelsior, showing the ocelli. Natural size. (From Hall & Clarke) exhibit an inner circular depression described by Hall and Clarke as the eye. This is encircled on its outer edge by a conspicuous subsemicircular orbital ridge, but separated from the latter by a concentric level area bearing the same sculpture as the rest of the carapace. In much compressed or collapsed carapaces of S. cestrotus the eye presents an aspect very like that of this specimen of S. excelsior. In a few better preserved examples however [pl. 49, fig. 1,] the eye is highly prominent, looking like a bean lying on the carapace and the large semilunate visual surface surrounds a small, subcircular top area [pl. 50, fig. 1]. The logical inference hence is that the visual node of S. excelsior bulged in the same way and we have represented it thus in our restoration. The intense concentric wrinkling of the area within the orbital ridge in the specimen in the National Museum is direct evidence of the collapse of the visual node.
By analogy it would be necessary to infer that the central circular broken area in the eye of S. excelsior is the outer end of the palpebral lobe and the entire surrounding concentric area the visual surface. The latter part of this inference is at once invalidated by the fact of the extension of the surface sculpture upon the concentric area. The first part of the inference that the broken down inner circular areas were parts of the
