THE EURYPTERIDA OF NEW YORK 65 
A fairly well preserved genital appendage of a female Dolichop- 
terus macrochirus [pl. 44] has been observed by us. It is clearly 
built on the type of that of Eurypterus in showing the two invaginated 
median lobes with their bifid extremities. The organ was also, as in 
Eurypterus, of relatively large size. 
The genital appendages of Stylonurus are not known. 
The second sternite has also been found to bear a genital appendage 
in the females of Eurypterus, Hughmilleria and Dolichopterus. In Euryp- 
terus it consists of one short unpaired proximal and two long awl-shaped 
distal pieces, the whole being covered by the opercular appendage. In 
Dolichopterus we have seen the impression of two similar slender terminal 
pieces between the shorter hornlike terminal pieces of the opercular appen- 
dage, and therefore feel sure that it possessed an appendage of the 
second sternite like that of Eurypterus. In Hughmilleria the appendage 
of the second sternite has been fully described and figured by Sarle [op. cit. 
pl. 62, fg. 9, ro]. It is small and attenuate with a triangular base. 
Probably the second sternite of the female was also furnished with 
a small appendage in some of the other genera where it has thus far escaped 
observation. 
From present evidence it may be stated as a general proposition that 
there are two lines of development of the genital appendages of the oper- 
culum in the eurypterids, those of the Pterygotus group and those of the 
Eurypterus group. In the first, the appendage is composed of but one 
unpaired lobe, which may become more or less elaborated, as in Slimonia. 
In the second group two unpaired and two paired lobes are developed. 
There is little known as to the genital openings in the eurypterids. 
Woodward has figured [1872, p. 117, fig. 36] small openings on round 
tubercles on the basal triangular areas of the opercular appendages in 
-Slimonia, which he considers as ovarian openings. Laurie, however, has 
not mentioned or figured these openings in his investigation of 
Slimonia [1893] and their presence seems open to doubt, especially since 
no homologous apertures have been seen in the other genera. Neither have 
