NOTES ON RETICULARIAN RHIZOPODA. 47 



due to the partial collapse of the investment, as not unfre- 

 quently occurs in certain other chitino-arenaceous forms, 

 Trochammina macrescens, for example. The mammillate 

 orifices do not appear on the upper and lower surfaces, but 

 only on the peripheral portions of the test. 



The figured specimen is from the North Atlantic ('' Por- 

 cupine "), 109 fathoms. 



Genus — LITUOLA, Lamarch. 



In the ' Introduction to the Study of the Foraminifera,' 

 published in 1862, all the then-known Foraminifera having 

 sandy or composite tests are referred to three genera — Lituola, 

 Trochammina, and Valvulma, the last named being regarded 

 as an intermediate rather than as a strictly arenaceous type. 

 ToLituola are assigned all the rough arenaceous forms, what- 

 ever their external contour or the condition of the interior 

 of their chambers ; and to Trochammina those in which the 

 constituent sand-grains are small and incorporated by a 

 large excess of calcareous or ferruginous cement, a thin, 

 smooth, non-labyrinthic shell being the result. This simple 

 classification answered every end so long as the number of 

 forms to be accommodated and their known range of varia- 

 tion were comparatively limited, and there can be no doubt 

 that it touched the essential distinction between two of the 

 principal groups of this section of the Rhizopoda. But in the 

 present state of our knowledge it scarcely meets the require- 

 ments of the case. Not only have a large number of arena- 

 ceous species been found with generic characters very different 

 from those of either of the types thus defined, but the number 

 of new forms and varieties, possessing the same peculiarities 

 of shell-structure as Lituola and Troc/iammina respectively, 

 has been so multiplied that the subdivision of both groups 

 has become desirable, if not necessary. The arrangement of 

 the TrochanmiiticB is considered on a subsequent page, and 

 although I have but little that is new to bring forward relat- 

 ing to Litulola (proper), it is quite within the plan of the 

 present paper to state briefly the results which have been 

 arrived at from the study of the very large series of forms 

 furnished by the " Challenger " dredgings. 



Practically the genus Lituola, as understood in this country, 

 has been coextensive or thereabouts with Professor von 

 Reuss^s family Lituolidea, which is made to include four 

 genera, characterised as follows : 



1. Polyphragma^ Reuss. — Test adherent. 



1 Poli/phragma eribrosum, Reuss, as figured in ' Das Elbthalgebirge in 

 Sachsen,' Iter Th., 1872, p. 139, pi. 33, figs. 8 — 10, has an irregular, 



