On Splroclinjta (Trypanosoma) Balbianii, c&c. 493 



than the eye in tlie adult ; diameter of eye 3 to 4^ times in 

 lengtli of head, interorbital widtli 2\ to 2?^ times ; mouth 

 sliglitly inferior, with feebly developed lips, interrupted on 

 the chin ; barbels two on each side, anterior about as long as 

 eye, posterior 1 to 1^ diameters of eye, the distance between 

 them about ^ diameter of eye. Dorsal III 7-8, last sim})le 

 ray strong, bony, not serrated, nearly straight, or feebly 

 curved, | to once length of head ; free edge of the fin feebly 

 emarginatc ; its distance from the occii)ut less than its 

 distance from the caudal fin. Anal III 5, longest ray about 

 -g length of head. Pectoral | to | length of head, not 

 reaching ventral ; latter below anterior rays of dorsal. 

 Caudal peduncle 1| to 2 times as long as deep. Scales 

 32-36 '^-^, 3-4 between lateral line and ventral, 14-16 round 

 caudal peduncle. Brown above, silvery on the sides and 

 below ; three more or less distinct round blackish spots often 

 present on each side, the first and second just above the 

 lateral line, one in front and one behind the vertical of the 

 base of the dorsal, the third at the base of the caudal fin and 

 traversed by the lateral line ; these spots may be absent or 

 reduced to the one at the base of the caudal fin ; fins whitish, 

 without spots. 



This fish grows to a length of 125 mm., but is usually 

 smaller, about 100 mm. long. 



LVIIL-^:-Sj)irochjeta (Trypanosoma) Balbianii (Gertes), its 

 Movements^ Structure, arid Affinities / and on the Occurrence 

 of Spirocheeta anodontte {Keysselitz) in the British 

 Mussel, Anodonta cygnea. ^j H. B. Fantham, B.Sc, 

 Derby Researcii Scholar, University College, London ; 

 and St. Mary's Hospital Medical School. 



(Preliminary Account.) 



Introduction. 



There are few more interesting organisms at present under 

 investigation than those microscopic yet most active forms 

 known as Spirochaites, which lie near the border-line of 

 plants and animals. They are, indeed, veritable members of 

 llaickel's kingdom Protista, and it is still a disputed point 

 whether they are really Protozoa or Bacteria. 



