PLANKTON OF THE WOODS HOLE KEGION 
137 
Apparently none of the larger gastropods have free-swimming stages, the bulk 
of the summer forms coming from those minute species that live on the floating 
Fucus and Sargassum. The following gastropods were distinguished in surface 
collections of 1922 : 
But one Nudibranch moUusk has been recorded by Edwards from surface 
collections. This species {Facelina bostoniensis (Couthouy)) appears each spring, 
often in large numbers. This year it appeared on January 21 and continued to 
be taken until May. Upon examination many females were found to contain 
dozens of small larvae, which were very similar in form to the adults. Four other 
species were represented by single specimens taken during the year — Ehjsiella 
catvla (Agassiz), June 1; Doto coronata (Gmelin), September 6; Alderia harvardi- 
ensis (Agassiz), March 29; and family Dotonidas, November 8. 
Clione limacina (Phipps), a pteropod, is often taken in large numbers around 
Marthas Vineyard. It is a member of the oceanic plankton and is occasionally 
blown into Great Harbor during southern storms. ' The author has five records 
of its appearance in surface collections. The first four — September 10, 1888, 
March 20, 1896, April 28, 1911, and May 2, 1911— were taken by V. N. Edwards; 
the fifth, on May 3, 1918, by R. A. Goffin. Another pteropod {Heterofusus retro- 
versus (Fleming)) had been recorded once in local waters (Sumner, 1913a). A 
single specimen was taken in Great Harbor on January 12, 1924. 
The larval Pelecepoda present a most difficult problem to the plankton investi- 
gator. The early larvae all look alike and can be distinguished, with any degree 
of certainty, only by careful measurements. During the summer the author was 
able to make few such measurements and for that reason the results are very in- 
complete. The late larval stages are more easily distinguished. J. Stafford's 
excellent paper on bivalve larvae made the identification of these forms a rather 
simple matter. At this stage, however, the bivalves sink to the bottom and are 
taken in much smaller numbers. 
The most common pelecepods of this region live in the shallow waters of pro- 
tected bays and harbors. For that reason they are quickly affected by the increase 
in temperature during the spring. The length of time required for the ripening of 
the gonads is not known, but many larvae of Mytilus edulis were found early in 
June, 1922. Later in July larvaB of a slightly different shape were noted. These 
proved to be the young of both Venus mercenaria and Mya arenaria. Many 
Pecten larvae were taken near Block Island in September, but none appeared at 
Woods Hole. Mya, Venus, and MytUus remained throughout the summer and 
until late in the fall. By August 10 Mytilus had almost acquired the adult shape 
and appeared less frequently in the collections, although many were taken through- 
out November and December. By this time the larv^ had long since passed the 
Littorina litorea (Linnaeus). 
Bittium alternatum, Say. 
Astyris lunata (Say) . 
Skenea planorbis, Fabricius. 
A combellid, probably Anachis avara 
(Say). 
Tritonofusus stimpsoni (Morch). 
Triphoris nigrocinctus, Stimpson. 
Lacuna vincta, Montagu. 
A vitrineUid genus (?) . 
8242°— 25t- 
4 
