PLANKTON OF THE WOODS HOLE REGION 161 
PYCNOGONIDA AND XIPHOSURA 
Pyenogonids are not pelagic animals, but live on hydroids and among the 
alge, occurring in surface collections only when the objects to which they are 
attached float into the nets. For this reason they are usually taken during the 
summer months. Only one specimen appeared in collections made after October 
1. That was on March 29 of the present spring (1923), when a single Pallene 
brevirostris Johnston was observed. This species is very abundant in the im- 
mediate region of Woods Hole and occurred almost daily during July and August. 
Females carrying eggs were found on August 21. On October 1, 1922, a male of 
Tanystylum orbiculare Wilson appeared. This was the only member of the species 
taken during the past year. A specimen of an unidentified genus new to the 
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Vode 
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Bk BR ee 2.8 8 
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Fic. 61.—Occurrence of common larve of the tribe Fig. 62.—Occurrence of common laryz of the tribe 
Oxyrhyncha in surface collections of 1922. —-.—=, Cyclometopa in surface collections of 1922. ——, 
Libinia emarginata and ZL. dubia, species not dis- Cancer irroratus; —~—-, Neopanope texana sayi; 
tinguished; ———, Pelia mutica —.—, Callinectes sapidus 
region appeared in August, 1922, and on July 23, 1923, a single Anoplodactylus 
lentus Wilson. 
Limulus polyphemus deposits eggs on sandy shores below the low-tide line. 
There are not many such spots about the bay in the vicinity of the “Hole,” and 
for that reason few young are carried into Great Harbor. In certain localities, 
such as the sand flats at Duxbury, Mass., and Cold Spring Harbor, L. I., great 
numbers of the young forms in the so-called “trilobite” stage swim about at the 
surface. However, heavy shells prevent these animals from being very active 
members of the plankton, and consequently they are usually taken only in calm, 
shallow water. When disturbed, they become motionless and sink to the bottom, 
