REPORT ON THE SCHIZOPODA. 205 



Challenger specimens belong to two different species, to be described in the sequel. They 

 may easily be known by the following distinctive characters : — 



Eyes verj large. Antennal scale linear. Telson exceedingly narrow, truncate 



at tip, ......... S. thompsoni (M.-Edw.). 



Eyes comparatively small. Antennal scale rhomboidal. Telson linguiform, Avith 



apex rounded, . . . . . . . . S. gracilis, Dana. 



53. Siriella thompsoni (M. Edwards) (PI. XXXVI. figs. 1-24).- 



Cynthia sp., V. Thompson, Researches, p. 55, pi. vi. 



Cynthia thompsoni, M.-Ed wards, Histoire nat. des Crustac^s, t. ii. p. 462, pi. 



Siriella vitreu, Dana, United States Exploring Expedition, Crustacea, pit. i. p. 656, pi. sliii. 

 figs. 6, a-m. 

 ^ Siriella hrevij^es, Dana, United States Exploring Expedition, Crustacea, pt. i. p. 660, pi. xliv. 

 figs. 3, a-l). 



Cynthia inei-mis, Kroyer, Nat. Hist. Tidsskr., 2'^"' R»kke, Bd. i. p. 44, Tab. ii. figs. 6, a-rj (male). 

 1 Promysis /jalatliece, Kroyer, Nat. Hist. Tidsskr., 2''<='' Esekke, Bd. i. p. 59, Tab. ii figs. 8, a~k (female). 



Siriella edwardsii, Claus, Zeitschr. f. wiss. Zool., Bd. xviii. p. 271, pL xviii. 



Siriella thompsoni, G. 0. Sars, Preliminary Notices on the Challenger Schizopoda, No. 50. 



Specific Characters. — Form of body not very slender. Frontal projection acutely 

 pointed. Last caudal segment shorter than the two preceding taken together. Eyes 

 very large, with cornea greatly expanded. Antennal scale narrow, linear, apex somewhat 

 obhquely truncate. Proppdal joint of legs undivided, terminal claw of moderate length. 

 Telson exceedingly narrow ; apex truncate, with three small teeth between the innermost 

 pair of apical spines. Outer plate of uropoda much shorter than inner, witli close upon 

 six spines on the outer edge. Length attaining 10 mm. 



Remarks. — I cannot but assume, that all the forms described under the different 

 names referred to above, belong to one and the same species, and that this is the one 

 first described by V. Thompson as Cynthia sp., and afterwards more fully designated by 

 Milne-Edwards as Cynthia thompsoni. As the generic name Cynthia has been long since 

 applied to a form of Ascidians, that proposed by Dana must of course be retained for 

 the genus. Originally, the name Cynthia was only applied to the males, and Siriella to 

 the females, the sexual differences being unknown till fully elucidated by Professor Claus. 



Description. — The length of the largest example collected is about 10 mm., but most 

 of the specimens in the collection are much inferior in size, though some of them are 

 apparently adult. 



The form of the body (see PL XXXVI. figs. 1-3) is comparatively less slender than 

 in most of the other species, though not nearly so thickset, as represented in the jfigure 

 given by Dana of his Siriella vitrea, which form in my opinion is identical with the 

 present species. 



The carapace is very small, not covering by far the whole of the trunk, two segments 

 of which, and even a small part of a third, being exposed behind. It is evenly emarginate 

 posteriorly in the middle, and tapers a little anteriorly, hence not being broader in its 



