TROCHAMMINA. 71 



by poor, starved individuals, but such specimens cannot be ignored, as they exist in 

 considerable numbers in some localities side by side with those that are well developed, 

 and admit of no doubt as to their relationship. 



The general history of the genus Trochmnmlnu is given in the ' Monograph of the 

 Foraminifera of the Crag,' p. 25, and its structural features are minutely described in 

 Dr. Carpenter's "Introduction," p. 141. Messrs. Jones, Parker, and Kirkby's paper 

 on the " Permian Trochammina pusilla and its Allies," 1 contains a comprehensive summary 

 of what was known up to the date of its publication concerning the Palaeozoic repre- 

 sentatives of the genus ; and it is a matter of some interest, that of the four species to 

 which the memoir is chiefly devoted, three are now shown to have come down from 

 Carboniferous times. Still more striking is the fact that at least two of these, viz. Tr. 

 incerta and Tr. gordialis, are not only found in fossiliferous beds of many succeeding 

 formations, but may at the present day be collected, living, at moderate depths in our 

 European seas. 



The brown colour of the test in Trochammina, due to the ferruginous constituents of 

 the cement, is regarded by many as a character of almost generic significance ; it is 

 therefore necessary to remark, that the specimens from some of the Mountain 

 Limestone beds are nearly pure white, and the same is often the case in those from 

 Permian sources. 



Professor Reuss applies the generic term Ammodiscus to the Spirilline non-septate 

 varieties of Trochammina, and in this course he has been followed by some of his fellow- 

 countrymen. I concur, however, with Messrs. Parker and Jones in regarding any generic 

 or even subgeneric division of the group on this ground as undesirable. The distinction 

 rests on an artificial basis, or rather on an idea, and any arrangement L in which it is 

 adopted leaves the numerous intermediate and partially septate varieties, which appear 

 wherever Trochammina abound, quite unprovided for. 



TROCHAMMINA INCERTA (d'Orbigny}.' PI. II, figs. 10 14. 



OPEECULINA INCEETA, d'Orbigny, 1839. Foram. Cuba, p. -49, pi. vi, figs. 16, 17. 



CRETACEA, Reuss, 1846. Verstein. Bohm. Kreid., p. 35, pi. xiii, figs. 



64, 65. 



ORBIS 1NFIMUS, Strickland, 1848. Quart. Journ. Geol. Soc., vol. ii, p. 30, fig. a. 

 SPIRILLINA, sp., Jones, 1850. In King's Monog. Perm. Foss., pp. 1820; and ID 



Morris's Catal. Brit. Foss., 2nd edit., p. 42. 



1 'Ann. and Mag. Nat. Hist.,' scr. 4, vol. iv, p. 386, pi. 13. 



2 In the lists of synonyms of the present species and also of Trochammina gordialis and Tr. pusilla I 

 have made use of the materials collected by my friends Messrs. Jones, Parker and Kirkby for their paper 

 before alluded to on the "Permian Trochammina: " as far as they go, and am glad to make this practical 

 acknowledgment of the value of their labours. 



