zoology: marine ikvertebrates. 69 



Of other large gastropods, Bticcinum, undatum and Chrysodomus 

 decemcostutus should be mentioned. These may be found commonly 

 in the "storm zone," among the debris of the upper beach. Perfect 

 specimens seldom are thrown up. Almost always they are much dis- 

 solved, and riddled by the boring sponge Cliona sulphurea. Calca- 

 reous algae frequently cover them with an encrusting deposit. Hy- 

 dractiuia usually is found on those shells which have served as the 

 home of the hermit crab. Perfect specimens are common on the 

 coast of Maine, but seldom are seen on the Massachusetts beaches. 

 The egg cases are found occasionally on our shores. With the two 

 preceding species may be noted at times the smooth fusiform shell 

 of Neptunea curta {Fusus islandicus), but this is rare on Revere 

 beach. Purpura lapillus is found on the beach, but belongs prop- 

 erly to the rocky shores. 



Two species of Crepidula are common on the strand. These 

 are C. fornicata and C. plana, the latter usually attached to other 

 gastropod shells. C. fornicata is the more common, and specJimens 

 of considerable size and of all degrees of convexity may be ob- 

 tained. The coloration varies to some extent, as do also the thick- 

 ness and curvature. Frequently a series of shells may be found 

 attached to one another, making a solid pile ; but this is more fre- 

 quently met with on mud flats. The young of this species and of 

 C. plana show a beautifully coiled embryonic shell or protoconeh. 



Among the smaller gastropods always found abundantly on 

 the lower part of the beach, the commonest is Tritia trivittata. 

 This shell is recognized easily by its turreted spire and the strong 

 vertical varices cancellated by revolving lines which ornament 

 its surface. It occurs by the thousand, sometimes heaped up into 

 ridges parallel to the wave front, sometimes spread out over large 

 areas of the beach. Many of the shells will he found with a round 

 hole bored through them ; and this condition has been attributed 

 to Lunatia heros, one of the most voracious gastropods of our 

 shores (Gould). 



A somewhat larger, less delicate, and less strongly ornamented 

 shell, Ilyanassa obsoleta, may be found commonly associated with 

 Tritia trivittata, although it is more at home on the muddy shores 

 of estuaries and bays. With these occurs the small smooth 

 Lacuna vincta, usually in great numbers. It is seldom found alive 

 on the beaches, but living animals may be taken from the roots of 

 the Laminaria and other seaweeds, as well as from stones dragged 



