ON THE ANASPIDACEA, LIVING AND FOSSIL. 501 
The segmentation of Paranaspides corresponds exactly 
with that of Anaspides, but in Koonunga cursor there 
are only seven free thoracic segments, the anterior segment 
bearing the first thoracic limbs being definitely fused with 
the head, so that the segmentation agrees with the condition 
in the more primitive Amphipoda and Isopoda. 
Among the fossil Anaspidacea we meet with an interesting 
condition. In Prewanaspides there are seven large thoracic 
segments, and an extremely narrow segment in front, sepa- 
TeExtT-Fic. 4. 
Paranaspides lacustris. Head with first and second antenne 
in situ. 
rated from the head by a distinct groove (text-fig. 3). In 
Paleocaris, Gampsonyx, and probably Gasocaris there 
are also eight thoracic segments, the most anterior segment 
behind the head being narrow as in Preanaspides. The 
extreme narrowness of this segment suggests that it really 
does represent the single first thoracic segment which in 
Anaspides has invaded the head-region, and finally in 
Koonunga has become fused definitely with the head. 
Behind this rather problematical first segment the segmenta- 
tion of the body agrees perfectly in all the Anaspidacea, both 
