44 



Occurrence. I have met with this form in many different places on the 

 Norwegian coast, from the Christiania Fjord at least to the Trondhjem Fjord. 

 It is found, often in considerable number, within the branchial cavity of several 

 kinds of Ascidians. When loosened from its hold, the animal rests nearly 

 immobile on the bottom, lying on the one or other side. Only from time to 

 time it is seen slowly to bend its body and to move the antennas and legs, 

 without however thereby to be enabled to change its place in any perceptible 

 manner. 



Distribution. Coast of Bohuslan (Thorell), British Isles (Brady), coast of 

 France (Canu), Mediterranean (Buchholtz. 



10. Doropygus psyllus, Thorell. 



(PI. XXI). 

 Doropygus psyllus, Tliorell, I. c. p. 49, PI. VII, 9. 



Specific Characters. Female. General form of the body rather like that 

 in the preceding species, though perhaps still shorter and stouter. Incubatory 

 pouch of very large size and quite evenly rounded behind. Tail scarcely 

 attaining half the length of the anterior division, and, as usual, composed of 

 4 segments, the last of which, as in D. pulex, is cleft into 2 diverging trian- 

 gular lappets. Caudal rami still more slender than in that species, otherwise 

 of a very similar structure. Anterior antennae composed of 9 well defined 

 joints, the 1st of which is much the largest, occupying almost half the length 

 of the antenna, 2nd joint much shorter but nearly as broad, and gibbously 

 expanded in front, being armed with 2 short spines in addition to the setae; 

 the remaining part of the antenna abruptly much narrower and extending at 

 an angle to the first 2 joints. Posterior antennae very slender, exceeding in 

 length the anterior ones, with the terminal joint considerably produced and 

 somewhat curved, apical claw very small. Endopodal part of maxillae with 4 

 setae inside the base, terminal joint much larger than in D. pulex and of 

 rounded oval form, being fringed with 6 plumose setae. Anterior maxillipeds 

 about as in D. pulex. Posterior maxillipeds however more fully developed, 

 being composed of 2 well defined joints, distal joint however rather small, with 

 3 unequal setae on the end. 1st pair of legs about as in D. pulex, the succeeding 

 pairs however having both rami distinctly 3-articulate and rather slender, joints of 

 outer ramus remarkably produced at the end outside. Last pair of legs with 

 the distal joint comparatively narrower than in D. pulex, sublinear in form, 



