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BULLETIN OF THE BUREAU OF FISHERIES 
two occasions, August 5 and 16, and in the Sound on August 18 and September 21. 
A single specimen of Nectonema agile Verrill was found among much detritus after 
a hard wind on July 11. 
MOLLUSCA 
Gastropod larvae are found throughout the year in all surface collections from 
inshore waters. There is considerable doubt as to the percentage of forms whose 
early stages are free-swimming. Many species, such as Busycon canalieulatum 
(Say) and Buccinum undatum Linnaeus, secrete cases in which the young pass 
their early stages, emerging in the form of the adults. Others deposit eggs in jelly- 
like masses attached to the underside of rocks and on marine plants. Littorina 
palliata (Say) is an example of this type. Still other forms, such as L. rudis Maton, 
are viviparous. The eggs of all of these are never found floating, and the young 
normally do not appear in the plankton. Certain young after emerging from the 
egg cases may accidentally be carried along by the currents. This probably explains 
the presence of many species taken during the summer and fall. 
A fourth group of gastropods no doubt contribute the bulk of the planktonic 
larvae. This group, of which Littorina litorea and Lacuna vincta are examples, 
discharge their eggs directly into the sea water. In these two species each egg is 
especially adapted for floating by a surrounding ring of jelly, which gives the appear- 
ance of the trench helmets worn by the American soldiers in the late war. This 
device serves also as a means of protection. The eggs and free-swimming larvae 
are found in great numbers from March until July. This is also the breeding 
season of Littorina litorea in English waters, according to TattersaU, who made 
extended observations upon that species. Lacuna vincta also swarms in February 
and March, some eggs having been found as early as December by Sumner. The 
eggs of this species may be distinguished by a light greenish tinge. In March of 
the present year (1923) great numbers of Littorina eggs appeared daily and in- 
creased throughout April. None were found in collections of the previous June. 
There was a maximum of eggs identical to those of Littorina in the fall, which the 
author has not been able to identify. There can be little doubt that this floating 
condition explains the rapid expansion of Littorina litorea after it was once estab- 
lished on the western Atlantic coast. 
An interesting adaptation to pelagic existence is found in a larval vitrineUid, 
the species of which I have been unable to ascertain. Shortly after the nucleus 
has formed, a broad shield grows out as an extension of the shell. This shield 
appears like the wide brim of a straw hat and enables the larva to float. Later, 
as older specimens showed, the shield is lost and the young mollusk sinks to the 
bottom. It is an interesting adaptation and has never before, to my knowledge, 
been noted. 
In the summer of 1922 Dr. Paul Bartsch kindly aided me in identifying the 
gastropod larvae that appeared during June, July, and August. The many forms 
often bear no resemblance to the adults, but are identified by comparing the nuclear 
whorls. These never change and offer an excellent means of identification. The 
nucleus is now used as a basis for classification among adult mollusks also. 
