THE EURYPTERIDA OF NEW YORK 67 
tergites, as shown by uncompressed specimens [pl. 20, fig. 8] and by 
the common observation that in compressed specimens the sternites pro- 
trude on both sides from under the tergites [pl. 4, fig. 4]. Although there 
are but five sternites including the operculum corresponding to the six 
tergites of the preabdomen the former are relatively so much longer that 
they overlap each other with fully half their length. 
The sternites, the operculum included, bore the branchiae. Woodward 
was the first to observe platelike appendages of the sternites in Pterygotus 
which he described as lam- 
ellae, and Laurie observed oa 
appendages of the sternites Qe g 
in Slimonia which he desig- , “a 
nated as “ branchial lam- 
ellae.”” Holm found organs 
in Eurypterus correspond- 
ing to those described by 
Laurie, but considers them 
only as “‘ Kiemenplatten ”’ 
instead of ‘* Kiemenblat- 
ter,’ or as oval spongy 
thickenings of the outside _ 
Figure 22 Eurypterus fischeri Eichwald. Portion of 
of the thin, soft membrane one of the posterior sternites, showing anteriorly the very 
: delicate membrane of the interior side torn off and pushed 
on the upper side of the forward and exhibiting the oval attachment area of the 
sternite, which probably _ Bills. x3. (From Holm) 
served as attachment places to the branchial lamellae. He has also observed 
detached bundles of two or three extremely thin superjacent leaves which 
he considers with doubt as possible branchial lamellae. The ‘‘ Kiemen- 
platte”’ or “branchial plate’ exhibits a very characteristic structure 
consisting of one or two trunk veins running parallel to the longitudinal 
extension of the plate and from which smaller branches proceed [see text 
fig. aa). 
In our material we have frequently been able to see the impression 
of the “ branchial plates ’’ from the dorsal side, as in the fine specimen 
of Eusarcus [pl. 29]. Detached branchial plates have also been observed 
