I40 NEW YORK STATE MUSEUM 
abdominal segment had become reduced.”’ From this fact, and the absence 
in Limulus of anything comparable to the central lobe of the genital oper- 
culum, the higher state of development of the metastoma in eurypterids, 
and the higher specialization of the last pair of legs, it is inferred, that 
‘‘ Limulus represents a more primitive type in almost every respect except 
the fusion of the abdominal segments, and is to be related to the euryp- . 
terids not by direct descent, but through 
a comparatively unspecialized ancestor.”’ 
Our evidence is fully accordant with 
Laurie’s view of the early separation of 
the eurypterids and Limulus. Of especial 
importance in this regard is the occur- 
rence of a typical eurypterid in the Cam- 
bric era (Strabops). The ventral side of 
this form is still unknown and in view of 
its important bearing on the phylogenetic 
relations of the eurypterids with the limu- 
lids and scorpions, the elucidation of the 
character of its genital operculum is es- 
pecially desirable. At any rate, none of 
the eurypterids now known from the 
Cambric to the Permic even suggest any 
fusion of the abdominal segments such as 
distinguishes Limulus, while in the De- 
Figure 27 Protolimulus eriensis : : : : 
Williams. Chemung group, Erie county, vonic Protolimulus eriensis 
Pennsylvania. (From Hall and Clarke) Witliams, the abdominal segments are ap- 
parently already fused and the characteristic Limulus structure developed. 
With the conclusion that the limulids and eurypterids were probably 
separate in Precambric time, the question arises as to the date of separa- 
tion of the Scorpionidae from the eurypterids. The relationship of Scorpio 
to Limulus has been fully discussed, especially by Lankester, and is no 
‘longer doubted. That of Scorpio to the eurypterids has been more fully 
