WATERLIME GROUP. 417* 



Among the collections from Waterville there is a fragment preserving 

 four thoracic segments, the basal joints of the swimming feet, the post- 

 oral plate, and the remains of four smaller feet analogous in position to 

 those of Eurypterus, but more slender and with longer joints ; the thoracic 

 segments also are proportionally longer. The first of these preserves some 

 remains of the central organ noticed in Eurypterus. The bases of the 

 larger first joints of the swimming feet, and the bases of the smaller ones, 

 are serrate or toothed, and the place of the mouth is distinctly seen. 

 There are no evidences of the anterior chelate organs, designated antenna, 

 and it otherwise differs from the figures of Pterygotus {Himantopterus) as 

 given by Mr. Salter. At the same time the fragment affords scarcely suf- 

 ficient knowledge of the structure to separate it from that genus. 



A single small carapace from Litchfield, Herkimer county, preserves 

 very broadly oval eyes, which are situated on the antero-lateral margins, 

 and differing in no particulars, except their position, from the eyes of 

 Eurypterus : it has likewise two small central oculiform tubercles. I refer 

 this with doubt to the Genus Ptekygotus*. 



Pterygotus cobbi ( n. s.)- 



Plate LXXXIII B. Fig. 4; and Plate LXXXIV. Fio.8? 



Carapace and body unknown. The specimen is the free ramus of a chelate 

 appendage, consisting of a thin crustaceous substance ; it is broad and 

 flattened at its articulating extremity, gradually narrowing towards the 



• It is only as these pages are going through the press, that I have seen the monograph of Messrs. 

 Ilrxi-ET and Salter on the Pterygotus, published this year (1859); and I can only regret that I 

 could not hare seen this elalwrate work before preparing my own observations. Mr. Huxley has 

 taken great pains to point out the errors of Prof. Agassiz, and others who have preceded himself, 

 in reference to the location of the .separated fragments and the restoration of parts in this fossil; and 

 it would have been well had he made himself quite sure of the relative position of some parts in his 

 own specimens, before publi-shing these criticisms. The misinterpretation of the location and functions 

 of the thoracic joint and its central appendage, is an error of equal magnitude with any that he has 

 pointed out. Those who have been pioneers in a work of this kind, and who have pressed their way 

 into an unknown region where, before, there was no guide or landmark, should be judged leniently 

 by those who follow the same road, made bright with the records and studded with the beacons of 

 their laborious predecessors. 



[ Pal.«;ontolooy III.] 53 • 



