DESCRIPTIONS OF GENERA AND SPECIES 307 



Definition. 1 5 mm. in length ; oesophagus very distinct but shorter than pharynx. Hah. — 

 Europe. 



This species is the largest of the genus and completely transparent. 



Vejdovsky considei-s that the Ch. diaphanus of d'TJdekem (4), who described the 

 genitalia, is not the same species, but is Ch. cristallinus. Vaillant, by omitting this 

 particular reference from his list, seems to concur. I would point out that the ' yellow 

 globules ' described and figured by Dalyell are probably the ripe ova. The genital 

 organs of Gli. cristallinus are, however, unknown, and d'Udekem's Ch. diaphanus is 

 only 5 mm. long, which better suits Ch. cristallinus. I include N. scotica as 

 a synonym on the authority of Johnston, who regarded it as being, the same as 

 Daltell's N. lacustris. 



(3) Chaetogaster cristallinus, Vejdovsky. 



Ch. cristallinus, Vejdovsky, SB. Bohm. Ges., 1883, p. aao. 

 Definition. Length, 2—3 mm. Dorsal and ventral blood-vessels not continued into pharyngeal 

 region. Oesophagus as long as pharynx. Hab. — Europe. 



This species was first described, and was later (24) more fully described and figured, 

 by Vejdovsky. Vaillant regards, I think with some reason, Lankestek's Ch. niveus 

 as probably identical with this species. The principal reason for the identification is 

 the long oesophagus. The dorsal vessel of this species ends in a bunch of cells 

 abruptly; just before its termination it passes through a sling attached to the first 

 dissepiment. 



(4) Chaetogaster flliformis, Sghmarda. 



Ch. fiUformis, Schmaeda, Neue wirbell. Thier., I. ii, 1861, p. 11. 



Definition. Length, % mm. Prostomium well developied ; no missing ventral setae. Hah. — 

 S. America. 



This species is curiously intermediate between Nais and the typical Chaetogaster. 

 It has no dorsal setae as in Chaetogaster ; but it has a well- developed prostomium, 

 and no nan-ow oesophagus, in which points, of course, it departs from Chaetogaster. 



(5) Chaetogaster diastrophus, Gruithuisen. 



Ch. vermicularis, Geube, Arch. f. Nat., 1851, p. 353 (in part.}. 

 ? Ch. miilleri, d'Udekem, Bull. Ac. Roy. Belg., xxii., pt. ii, 1855, p. 554. 

 Nais diastropha, Gruithuisen, Nov. Act. Nat. Curios., 1828, p. 417. 



R r 2 



