METAZOA MOLLUSCA. 223 



Fulgur (Nos. 462-465, F. canaliculatum Say), places its 

 eggs in horny sacs or capsules which it fastens together in a 

 long string (No. 463; see lowest shelf). These maybe 

 opened and the young (No. 462) observed in different 

 stages of development. The specimens possess a smooth 

 rounded protoconch, so thin and translucent as to show 

 the yellow body within. The succeeding whorl is ribbed, 

 and extends into a long canal giving the shell a pear-like 

 shape which remains essentially the same in older stages 

 (Nos. 464, 465). The model (No. 465, placed on account 

 of size at the back of the Section on the right) shows the 

 large foot extended as in the act of crawling ; the head 

 with its tentacles ; the mantle on the edge of the shell ; and 

 the siphon in the long canal. 



Fasciolaria is nearly related to Fulgur and its exquisite 

 egg cases are seen in No. 466 (see erect portion of Sec- 

 tion) . This species (F. tulipa Linn.) fastens these flower- 

 like cases to some foreign object, coral in this instance. 

 Across the free end of the tube, stretches a membrane 

 which opens when the young are ready to escape. 



Magilus antiquus Mont, is a reduced form, the reduc- 

 tion being due most probably to the habit of living 

 in coral. The young shell (PL 467) is a thin spiral of 

 three or four whorls, proving that its more immediate 

 ancestors had a spiral shell. The latter is similar to 

 that of Natica, Buccinum, and the like, and for this reason 

 it is placed near them. In order to keep on a level with 

 the surface of the growing coral, Magilus ceases to revolve, 

 and puts out a long, nearly straight tube (No. 468). As 

 it advances with the new growth it fills up the spiral and 

 tube behind it. 



The veliger stage of Astyris (Pis. 469, 470, x 100 

 diameters ; the colors are schematic), shows the large 

 lobed, ciliated velum, so characteristic of this stage of 

 Gastropods, and the spiral shell. The adult (No. 471) 

 has a shell with few whorls. The model represents the 

 animal as walking on the sand with extended foot, ten- 

 tacles, and siphon. 



