156 MR. H. CHARLTON BASTIAN'S MONOGRAPH 



the posterior, which is sharp and filiform. Head bluntly rounded, furnished with a circlet 

 of 4-6 short seta?. Integument having very fine transverse striae, about awoo" apart. 



Pharyngeal cavity very small, conical. CEsoj:)hagKs about ^th of total length, en- 

 larging very slightly backwards. Intestine sparingly covered with non-tessellate he- 

 patic granules. Anns -aou" from posterior extremity. Ocelli two highly refractive yel- 

 lowish bodies, with a dark central spot on dorsal aspect at -gwo" ffom anterior extremity. 

 Vulva behind centre of body. 



Male, length -:^", breadth 9-^". 



(Esophaffiis relatively shorter. Amis 2^2" from posterior extremity. Spicules barbed 

 at upper extremity, curved, y^oo" loiig 5 accessory pieces lying nearly at right angles 

 to spicules, pointed. 



Mab. Small green filameutous weed from tide-pools, Ealmouth. Also observed in a 

 small aquarium for two or three weeks, feeding on minute vegetable spores near the 

 surface of water. 



2. T. PARVUS, n. sp. (Plate XIII. figs. 185, 186.) 



Female, length -^", breadth j-^s o'- 



External Characters. — Body tapering at both extremities, especially at posterior, 

 commencing behind vulva. Head truncate, naked. Striae of integument imperceptible. 



Pharyngeal cavity indistinct. (Esophagus about -yth of total length. Intestine 

 sparingly covered with hepatic particles. Anus 3^5" from posterior extremity. Vulva 

 posterior to middle of body. Ocelli 



Ifale, not seen. 



SaL Small green weed from tide-pools, Falmouth. 



23. THERISTUSi, Bastian. 



Gen. Char. Body tapering at extremities. Caudal sucker small ; sucker-tubes not 

 visible. Integument having transverse striaj; lateral, circular, convex prominences 

 close to anterior extremity; cephalic setae, but no papillae. Pharyngeal cavity 

 . moderately large, rounded ; parietes membranous, not horny. (Esophagus distinctly 

 muscular, nearly cylindrical. Intestine plentifully covered with hepatic particles, more 

 or less tessellate, and of a brownish colour. Vtilva at commencement of posterior 

 third of body. Uterus unsymmetrical. Spicules shaped like a reaper's hook. Ac- 

 cessory jyieces two thin rounded plates directed backwards. Ocelli none. Vaginal 

 glands two, unequal, pyriform. Excretory ventral gland .... Lateral canals . . . ., 

 Movements very active. 



1. T. ACER, n. sp. (Plate XIII. figs. 187-188.) 



Male, length ^5", breadth 4^". 



External Characters. — Body tapering at extremities, slightly forwards, but gradually 

 narrowing to a point posteriorly. Head rounded, furnished with about eight spreading 

 setae, arising from swollen bases. Integument having transverse striae, xTooo" apart ; 

 conical projections 3x33 " ^^ diameter, at T-2V0 ' from anterior extremity. 



' Oepiarfis, a reaper, on account of the shape of the spicules. 



