CRUSTACEA. 139 



Observations. This species does nol widely differ from the Proetus Macrobius, 

 of Billings, from the Lower Helderberg of Square Lake, Maine. The latter 

 species, however, is of considerably larger size, and also differs in the following 

 particulars, viz. : the frontal area is not concave: the glabella is Longer; the 

 axis of the pygidium bears fewer annulations, and the surface of both cephalon 

 and pygidium is smooth or minutely punctate. 



This rare species is known in only a few specimens of the cephalon and 

 pygidium. One example shows the two parts in juxtaposition, and from this 

 fact, and from the analogy of other species of this genus, it is more than 

 probable that they belong to the same species and the same individual. 



Distribution. Lower Helderberg group. In the shaly limestone: Near Clarks- 

 ville, Albany county. 



PHAKTHONIUES (?) DENTICULATUS. 



PLATE XXV, FIGS. 14, 15. 



Proetus (Phatton) denticulatus, Meek. U. S. Geol. Expl. Fortieth Parallel, part 1, Palaeontology p. -Ill ; pi 



i, fiys. 10, 10 a, 10 b. 1877. 



Certain fragments, consisting of the pygidium, the glabella and detached 

 thoracic segments, were described by Mr. Meek under the above name, and 

 though the different parts may not have all belonged to the same species, the 

 pygidium, which the author accepted as the type of his description, appears to 

 represent a member of the genus Phai'thonides. The original specimens have 

 not been accessible for examination and comparison, and we therefore repro- 

 duce the original description of the pygidium, accompanying it with figures 

 copied from the work cited : 



"Pygidium transversely sub-elliptic, and nearly twice as wide as long, with a 

 moderate convexity. Its mesial lobe is about as wide anteriorly as each lateral 

 lobe (exclusive of their lateral spine-like projections), and more prominent than 

 the latter, with three or four segments. The lateral lobes are rather depressed 

 and show about four segments each ; these segments are not well defined, but 

 have each a distinct mesial furrow, extending out to the margin, where each 

 segment terminates in a short spine directed backward ; while there are two 

 other smaller spine-like projections just behind the posterior end of the mesial 



