294 University of California Publications. [Zoology 



ticm of the pedicel the prisms which are thin-walled elsewhere 

 In. mum. very thick-walled so that their central cavities are almost 

 obliterated, giving a pitted appearance to the wall in this region. 

 This wall is, as before stated, much thickened, but I have found 

 only a single layer of prisms in it. It has a yellowish brown 

 color which is in strong contrast with the hyaline character of 

 the rest of the lorica. The presence of rings on the lorica of 

 Ibis species and the occurrence of lorieae Inning only one or 

 two rings raises an interesting question as to the method and 

 significance of their formation. It seems probable that there 

 occurs during the period of lorica formation a temporary 

 suspension in the factors leading to its elongation without con- 

 current diminution in the supply of the materials from which 

 the hexagonal prisms are formed, resulting in a local aggrega- 

 tion of the prisms in a ring. This process may. it seems, occur 

 two or three times and at an approximately uniform interval. 

 The structure in these particulars is probably correlated with 

 some phase of activity of profound importance in the animal's 

 economy which is subject to rhythmic repetition. Naturally 

 the suggestion arises that division or possibly conjugation may 

 afford the basis on which these features of shell structure rest. 

 Observations on this point are lacking because of the great dif- 

 ficulty of keeping these most delicate pelagic organisms under 

 laboratory conditions. 



The animal has not been seen in a normal condition. Mori- 

 bund individuals have three or more ellipsoidal nuclei. 



Dimensions. — Total length, -105/u.; diameter of oral end, 

 70 ju ; length of terminal spine, 35 /a ; width of face of pedicel, 

 20 ju ; diameter of rings 82 /a ; thickness of wall, 6-8 /u; diameter 

 of prisms, 2-4 /x. 



This species has been found generally in the plankton of 

 the Pacific off San Diego at all seasons of the year but more 

 frequently in the summer. It is never very common and is 

 more frequent in vertical catches than in those taken at the 

 surface. It appears to be a eupelagic species. 



