APPENDIX. 749 



sponges. It is possible that the spicula of allied species may have contributed 

 to deep-sea formations in ancient oceans. (See figs.y, I, m, p. 271.) 



Figs. 980-982 are of Poly cystines from tbe Barbadoes (p. 612); fig. 980, 

 Lychnocanium Lucerna Ehr.; fig. 981, Eucyrtidium Mongoljieri Ehr.; fig. 982, 

 Halicalyptra Jimbriata Ehr., the first two magnified 100 diameters, the last about 

 75. Erom these deeply concave forms there are gradations in one direction to 

 disks with concave centres, and to flat disks, both with plain and pointed borders, 

 and in the other direction to elongate, conical, and spindle-shaped forms. 

 Others have the shape of a flattened cross ; another is an open diamond with 

 narrow diagonals and periphery. The disks have a concentric, and not a spiral, 

 structure, and thus are unlike those of Nummulites. For figures, see Ehren- 

 berg's Mikrogeologie, and Bailey in Amer. Jour. Sci. [2] xxii. pi. 1. 



The living Polycystines extend out fibre-like processes through pores in the 

 shells, and in this respect are like Rhizopods. 



Although probably among the earliest kinds of life, Polycystines have not 

 yet been recognized in rocks below the Tertiary, unless an ovoidal siliceous cell 

 found by M. C. White in the chert of the Black River limestone of Watertown, 

 N.Y. (Amer. Jour. Sci. [2] xxxiii. 386, fig. 30), is of this nature. 



2. Malacozooids; or, Mollusk-like Protozoans, as the Rhizopods. The mine- 

 ral secretions, when there are any, are calcareous, and the cells are arranged 

 alternately or spirally (p. 164), in this resembling the Bryozoans and Gastero- 

 pods among Mollusks. 



D'Orbigny's classification of the Rhizopods, given on page 164, is not a natural 

 one; and none has yet been proposed tbat is free from objections. 



3. EntomozoOIDS ; or, Articulate-like Protozoans. 



The Infusoria that are not plants nor larval forms of higher species belong 

 to one of these three divisions. According to Agassiz, the Vorticella group is 

 related to the Bryozoans among Mollusks. Other Infusoria, as the unsymme- 

 trical Trachelocercse, Plesconise, etc., may be also Mollusk-like forms. Many of 

 the symmetrical Infusoria have been proved to be only the embryonic condition 

 of worms; but some so related will probably prove to be true Entomozb'oids. 

 The Arncebse, as has been suggested, may be* larval, as is now known to be the 

 case with the Gregarinidse. 



The geological importance of Rhizopods has already been explained, except- 

 ing in one respect, — their connection with the origin of Green-sand, a fact first 

 observed by Ehrenberg. The Green-sand grains of the Cretaceous and other 

 formations are found to be very generally casts of these shells. The material 

 first forms within them, and then penetrates all the pores of the minute structure, 

 and finally, on the disappearance of the carbonate of lime, it has their interior 

 or exterier form. Bailey found this same green earth (glauconite) filling recent 

 Rhizopod shells from the Gulf of Mexico, and from the bottom of the Atlantic 

 beneath the Gulf Stream and in other parts ; and Pourtales has since made the 

 same observation. The latter states, however, that he found this green earth 

 penetrating also the shells of some small Mollusks, Barnacles, and Millepore 

 Corals. No chemical explanation of these facts has yet been offered. (Bailey, 

 Amer. Jour. Sci. [2] xxii. 282; Pourtales, Rep. Coast Survey, 1859, 248.) 



