THE FAMILY ASTKOKHIZID^ 109 



deep-water habits, have been discovered only of 

 late years, comparatively speaking, by the modern 

 methods of deep-sea dredging, the operations of 

 which have effectually proved that almost every 

 part of the ocean floor is the habitat of living 

 organisms. 



One of the most noteworthy forms in this family 

 is that of the genus Asfrorhiza, which, as a 

 central type, has been taken by Brady to indicate the 

 general character of the whole group. A shallow- 

 water species of this genus was discovered as far 

 back as 1857 by Sandahl, who found his specimens 

 of A. limicola, as the species is named, off the coast 

 of Sweden. This is, however, one of the exceptions, 

 since the majority are found in deep water, and to 

 this exceptional occurrence the early discovery of 

 the genus is due. 



The Astrorhizids are for the most part irregular 

 in form, or at all events do not show the same 

 symmetry as members of other families of the 

 Foraminifera. A special feature in the construc- 

 tion of the test is that, notwithstanding the rough 

 exterior, the inside is, we may say, invariably 

 smooth, and often quite glazed or polished with 

 the sarcodic or chitinous cement ; reminding one 

 in this respect of the internal surface of molluscan 

 shells where in contact with the mantle of the 

 animal. 



The genus P^aiinnospluera is one of the simplest 

 types of the AsTROKmziDyE, consisting of a single 

 globular segment enclosed in a rough sandy test, 



