OF THE PROTOZOA. RHIZOPODA. 231 



A limited distribution, both in reference to place and to the conditions of 

 existence, has been determined by Ehrenberg and other observers of the Poly- 

 thalamia, and also employed by geologists in fixing the period of the deposi- 

 tion of certain strata, and the circumstances under which it has occurred. 

 Thus Bailey records of the Atlantic soundings, that they " contain no species 

 belonging to the group AgatMstegia (D'Orbigny), a group wliich appears to 

 be confined to shallow waters, and which in the fossil state first appears in 

 the tertiary, where it abounds." Again, they " agree with the deep soundings 

 off the coast of the United States, in the presence and predominance of species 

 of the genus Glohigerina, and in the presence of the cosmopolite species Orbu- 

 lina universa (D'Orb.) ; but they contain no traces of the Margimdina Bachii, 

 Textilaria Atlantlca, and other sj)ecies characteristic of the soundings of the 

 Western Atlantic. In the vast amount of pelagic Foraminifera, and in the 

 entire absence of sand, these soundings strikingly resemble the chalk of 

 England, as well as the calcareous marls of the Upper Missoiui ; and this 

 would seem to indicate that these also were deep-sea deposits. The cretaceous 

 deposits of New Jersey present no resemblance to these soundings, and are 

 doubtless littoral, as stated by Prof. H. D. Rogers." 



A fijj:ed geographical distribution is also implied by the division made by 

 D'Orbigny of the sj^ecies he observed, — viz. into 575 peculiar to the torrid 

 zone, 350 to the temperate, and 75 species to the frigid zone. Moreover, Dr. 

 Carpenter stated (in the Annual Addi'ess at the Microscop. Soc. 1855) that 

 he and Prof. Williamson find " that there are certain species whose range of 

 distribution is limited, and whose form is remarkably constant, but that, in 

 by far the greater number of cases, the species of Foraminifera are distributed 

 over very wide geographical areas, and have also an extensive geological 

 range." Mr. Jeffreys remarks that, in his opinion, <' the geographical range, 

 or distribution of species, is regulated by the same laws as in the Mollusks and 

 other marine animals. I have found in the gulf of Genoa species identical 

 with those of our Hebridean coast, and vice versd.^^ 



Fossil Foraminifera. — In a fossil form the PolytJialamia are very common, 

 and enter largely into the formation of several rocks, chiefly calcareous or of 

 the tertiary series, m every part of the world. Ehrenberg, in his microscopic 

 examination of the chalk formation, represents these shells as the most im- 

 portant constituent ; and Dr. Bailey speaks of them as largely concerned in 

 the formation of the tertiary rocks of South Carohna, and adds, they '*are still 

 at work in countless thousands on her coast, filling up harboui^s, forming 

 shoals, and depositing their shells to record the present state of the sea- 

 shore, as theii^ predecessors, now entombed beneath Charleston, have done with 

 regard to ancient oceans. For the city just named is built on a marl 236 feet 

 thick. The marls from the depth of 110 to 193 feet are tertiary, as also, 

 in aU likelihood, are those beneath, extending from 193 to 309 feet, and also 

 of the Eocene epoch. The lithological characters of the marls from 236 to 

 309 feet differ from those above them, although many of the same species are 

 stiU to be detected " {A. N. H. 1845, vol. xv.). 



The most abimdant Foraminifera of the chalk belong to Eotalia, Spirulina, 

 and Textilaria : the fossil genus Nummulina abounds in tertiar}^ strata ; and 

 their shells constitute the chief ingredient in the composition of many lime- 

 stone rocks used in building, such as those in Egypt, from which the huge 

 stones of the Pyramids are quarried. In America this genus is largely re- 

 placed, as a component of limestone, by the genus Orhitoides. Species of 

 Textilaria are the most abundant in Oolitic formations. In the cretaceous 

 earths, says D'Orbigny, genera and species augment in rapid progression from 

 the lower to the higher formations. On arriving at the tertiary rocks, Fora- 



