TEIOUSPIDARIA. 131 



is here figured, may be briefly described as follows : — Head 

 triangular, flat, supported by a narrow neck, wliich increases 

 rapidly in breadth, and is marked by numerous extremely fine 

 transverse stride ; bothria, two in number, compressed laterally, 

 narrow, supported on two sessile petaloid appendages, the latter, 

 uniting at the summit of the head, to form, in profile, a semi- 

 circular festooned border ; mature segments i^ to | of an inch 

 deep, by ^ an inch in breadth, displaying ten or twelve longitudinal 

 furrows, whilst their inferior borders overlap each succeeding joint ; 

 reproductive orifices conspicuous, in the mesial line ; length of the 

 strobila upwards of one hundred inches. 



Tricus2ndaria. — Of this genus there is but one species known 

 — under the synonym Tricenophorus nodulosus — ^but it is widely dis- 

 tributed amongst our fresh- water fishes. It varies in length fi^om one 

 to two feet, but is seldom more than | of an inch in breadth. The 

 segmentation of the strobila is very indistinct, but the reproductive 

 organs occur at regular intervals. All parts of the body are 

 extremely contractile, and this is particularly the case with the 

 head, which at diff'erent times presents very various forms. I notice 

 the worm in this place chiefly with the view of again calling atten- 

 tion to certain pecuharities which I observed in a juvenile specimen 

 obtained from the stomach of a pike. The points in question have 

 reference to the cephalic hooks and calcareous corpuscles. It has 

 not been generally noticed that the tricuspid hooks support thin 

 chitinous laminge, which connect the two lateral horns of each 

 hook to the central apophysis. The object of this arrangement is 

 probably to afford additional security to the prong-like processes, 

 thereby rendering them capable of greater resistance ; but what- 

 ever signification or use they may possess, their aspect curiously 

 resembles the aortic valves of the human heart. As I have else- 

 where remarked,* Van Beneden appears to think it an error that 

 the cusps of the hooks should have been figured in the " Regne 

 Animal," as directed forwards, and has himself, consequently, 



* " Microscopical Journal," for 1850, p. 202. 



