74 MARINE INFUSORIA. 



matter brought by the dredge from the sea-bottom. By the use of the 

 towing-net, employed, however, on one occasion only, and when the 

 elements were by no means propitious for such operations, the sniall 

 minority, including, as it eventually proved, the most interesting capture 

 of the series, was secured. The contents of the net, as emptied on board 

 the steam-boat into the glass receivers, were by no means promising, 

 consisting merely of a little flocculent matter, at first distributed 

 indifferently through the mass of water, but which, after a short interval, 

 collected at the surface in the form of a pale yellow unsubstantial scum. 

 Specimens of this scum examined fresh, and permanently mounted, 

 both on board and later on in the evening, on our return to Falmouth, 

 demonstrated that almost its entire mass was composed of two minute 

 pelagic diatomaceous types. One of these, (Plate IV., Figs. 17 to 19,) 

 forming substellate or long spiral and corkscrew-like aggregations, each 

 component frustule having a somewhat inflated triangular body, and a 

 long median and spine-like apical prolongation, is apparently identical 

 with, or closely allied to, Asterlonella Bleakeleyii. In no account of the 

 several species of this same genus, at this moment accessible, however, 

 do I find any record of their formation of long symmetrically twisted 

 spiral aggregations, which in the present case is so eminently 

 characteristic of the f ally developed and perfect organism. The second, 

 but less dominant diatomaceous type, accords essentially with the 

 figures and descriptions given of Rhizosolenia setigera, consisting of 

 perfectly straight, attenuate cylindrical frustules, chiefly remarkable for 

 their finely produced and needle-like axial terminations. In some of 

 the larger frustules a single or double spiral pattern was faintly 

 discernible. 



A more leisurely examination of the mounted slides of these 

 diatomaceous skimmings has led to the detection among the same of the 

 three infusorial forms placed first on this list. All these are, like the 

 diatoms, essentially pelagic in their habits, and, possessing in each case 

 an indurated lorica or carapace, adapt themselves readily for permanent 

 preservation. 



1. — Dictyocysta cassis,KM., (Plate TV., Figs, land 2.) — Of this type, the 

 most interesting capture on my list, unfortunately only the empty test 

 or lorica has been preserved. The form and structure of this skeletal 

 element are, however, so definite and characteristic as to leave no doubt 

 whatever regarding the nature and relations of its former occupant. 

 The lorica, which resembles in shape a conical cap or helmet, is of 

 silicious consistence, perforated throughout with closely-set, irregular, 

 polygonal foramina, and, in the absence of the knowledge that has 

 recently come to hand, would be regarded as the silicious test of one of 

 the simpler pelagic Radiolaria, and be referred in that same group to 

 Ehrenberg's Polycystine genus, Dictyocysta. Professor Hoeckel, however, 

 has lately shown in an account of some new pelagic Infusoria, published 

 in the " Jenaiscbo Zeitschrift," for the year 1873, that the original 

 fabricators and inhabitants of these elegant helmet-shaped tests are not 

 Jladiolaria, but belong to the more highly organised group of the Ciliato 



