232 INVERTEBRATA OF MASSACHUSETTS. 



This shell is distinguished from all others by its inflated, globular 

 appearance, and its simple, deep umbilicus. It very much resembles 

 an Ampulla RiA, and is most probably the N. ampuJluria of Lamarck. 

 It also grows to a larger size than any other known species. I have 

 one specimen the greatest length of which is 4;^ inches, and greatest 

 breadth 3^ inches ; and I have seen one 5 inches by 3f inches. The 

 shell is light for its size, and its whole structure and appearance are 

 very simple. 



This, in common with other species of Na'tica, is very voracious, 

 and plays a conspicuous part in devouring the dead fish and other 

 animals which are thrown up by the tide. Many of the shells thrown 

 upon the shore are found to be perforated with a small round hole. 

 This is done principally by the difl^erent species of Na'tica, They 

 have the power of perforating shells, it is generally supposed, by dis- 

 charging an acid which decomposes the shell ; and through the aper- 

 ture they extract the juices, and destroy the lives of the otherwise 

 secure inhabitants. Their foot is very large, so as completely to en- 

 velope the objects on which they prey. In moving, they burrow in 

 the sand, so as to be almost entirely concealed by it, and their place 

 is generally indicated by a small heap of sand. 



The singular nidus, in which the animal of Na'tica deposits its eggs, 

 has been an object of much curiosity and speculation. It is a mass of 

 sand glued together into the shape of a broad bowl, open at the bottom, 

 and broken at one side. Its thickness is about that of an orange-peel, 

 easily bent without breaking when damp, and when held up to the 

 light will be found to be filled with little cells arranged in quincunx 

 order. Each of these cells contains a gelatinous egg, having a 

 yellow nucleus which is the embryo shell. It is found plentifully at 

 midsummer, on every sandy flat where any species of Na'tica resorts. 

 It has passed under many names, and its true nature seems to have 

 been first suspected by Mr. Boys, who gave a description and plate of 

 it, in the " Linnaean Transactions," vol. v. 230, pi. 10. In the 14th 

 volume of the same work, Mr. Hogg fully demonstrated its character, 

 by hatching, from those found on the English coast, the young of 

 Ndtica gluucina. 



To show what a puzzle it has been, I will add some of its names 

 found in books. 



Flustra arcnosa. Ellis ; Zooph., and also his Corallines, pi. 25, f. e. 



Fhistre areneuse, Lamouuoux ; Pulijp. jltx. Ill, No. 220. 



riustre arenacee, Blainv. ; Dirt, des Sc. A'lit-, and Man. (TActinoL, 446. 



