4 
CRETzVCEOUS CTLTOPODA 
'rhc primary division of the class is, according to the arrangement of the 
tentacles, in a single ring at the edge of the anterior end of the cell, or situated on 
special horsc-shoe-shaped arms ; the former constitute the GvMh'OLAiMATA, and are 
mostly marine ; the latter, the F jiylactol^mata, all of which arc fresh water 
inhabitants. 
The former sub-class is separated into 1st, the Falvdicellaea, which possess an 
imperfect evagination of the tentacular sheath, and are all fresh water forms ; 2nd, 
the Cjieilostomata with perfect evagination, (as have also the following) : the cells 
urceolate or depressed, ovate, with a contracted aperture, placed at or near the 
anterior end, narrower than the diameter of the coll, and generally closed by a 
moveable lip or muscle ; Brd, Ctenostomata, with tubular or depressedly ovate cells, 
the apcrtiu’c fiu’nished with a setose fringe for its closure. The propriety of this 
division as distinct (in part) from the next and the preceding appears to me 
doubtful, at least as regards the species with ovate cells ; there are a great many 
Celleporce witlr a fringe of spines round the aperture, these being either horny 
and flexible, or calcareous. The Mli division constitute the Cyclostomata, with 
perfectly tubular cells terminating with a simple aperture of the same or very nearly 
the same diameter as the cell itself. 
In a pahcontological point of view, the Creilostomata and the Cyclostomata 
only arc of importance ; they arc hotli marine, and their cells are mostly calcareous, 
or semi-calcarcous, rarely horny, and very rarely v'ith a fleshy ectocyst. The 
Cyclostomata arc decidedly the more lowly organised ones, and occur from the 
palajozoics upwards up to the present time, while the Creilostomata are scarcely 
kno^vn before the Jurassic period. But almost throughoiit the mesozoic ej^och the 
former order considerably exceeds the latter, both as regards genera as well as 
species. In the kainozoic epoch the two orders almost balance themselves in number 
of genera, but the Creilostomata appear to have a larger number of species. 
In tbo present epoch the preponderance of the last over the former is still more 
marked. 
As regards distribution in space, it is a noticeable fact that the colder and 
temperate regions are richer in Ciliopods than the tropic ones, but it is not 
correct to suppose that they are wanting within the tropics, though they are 
unquestionably rare, at least within the laniinarian zone near the eqixator. hat 
deep dredgings in the tropics would reveal, it is diflicult to jn’edict. In the northern 
and temperate seas many species were found up to the greatest depth, to which 
dredgings have been carried on, and animal life discovered. How flxr we arc 
allowed to apply general results of our observations regarding the distribution ot 
the Ciliopods in the lu’csent seas to their distribution in former geological periods 
must be determined by continued and prolonged observations. But according to 
our present knoAvlcdge, it seems certain that both cretaceous and tertiary dejxosits, 
Avhich are geographically situated nearer to the poles, are richer in Ciliopods than 
deposits of the same age situated nearer to the equator. 
( 38 ) 
