98 



THE VOYAGE OF H.M.S. CHALLENGEE, 



structure of the gills the geuus shows marked difTereuces as compared with other 

 EuphausiidjB. In addition to the typical species first described by Milne-Edwards, 

 three other very distinct species, apparently belonging to this geuus, are represented in 

 the Challenger collection, and will be described more in detail in the sequel. I give here 

 a synopsis of the four species as yet known to lielong to this genus. 



Carapace - 



with two strong lateral denticles. liostral projection sharply pointed, 

 and having posteriorly at its hase a flattened, forward-pointing 

 spine. Tail with the four hind segments produced posteriorly to 

 short dorsal spines, ...... 



with a single lateral denticle. Kostnnn short, acuminate. Carapace 

 and tail smooth above. Eyes remarkably small, . 



without any 

 lateral denticles. < 

 Frontal part 



obtusely rounded. Caudal segments smooth 

 above, ..... 



produced to a distinct compressed rostrum and 

 having an elevated crest above. Fourth and 

 fifth caudal segments jjroduced posteriorly to 

 small dorsal denticles, 



T. trimspidata, M.-Edw. 

 T. microphtlialma, n. sjj. 

 T. oUit^ifrons, G. 0. Sars. 



T. cridata, G. 0. Sars. 



25. Thysanopoda tricuspidata, Milne-Edwards (PL XVII.). 



Thysanopoda tricuspid<da, MUne-Edwards, Ann. d. Sci. 'KaX., t. xix. ji. i.')!, pi. xix. 

 Thysanopoda trku><pidata, SI ilne-Ed wards. Hist. nat. des Crustaces, t. ii. p. 463, pi. xxvi. 



figs. 1-6. 

 Thysanopoda tricnupidata, G. 0. Sars, Preliminary Notices on the Challenger Schizopoda, No. 24. 



Specific Characters. — Body rather slender, with the tail slightly bent in the middle. 

 Carapace armed with two strong lateral denticles at the inferior margin ; frontal part 

 produced to a sharp-pointed rostrum, and having above, in the middle, a flattened 

 anteriorly directed spine. Third caudal segment projecting posteriorly as a strong 

 dorsal spine ; the three posterior segments armed with similar, but much smaller spines. 

 The two anterior pairs of caudal epimera curved anteriorly ; first pair very large and 

 divided into two acuminate lappets. Last segment rather elongate ; preanal spine 

 bidentate. Eyes large and projecting, pyriform. Antennular peduncle slender, 

 cylindrical, with a small narrow lanceolate lappet at the end of the first and second 

 joints above. Antennal scale oblong-linear, apex narrowly rounded, outer corner 

 jutting out as a small denticle. Penultimate pair of legs much smaller than preceding. 

 Telson with four pairs of dorsal denticles, apex greatly produced, and armed close to the 

 tip with two pairs of exceedingly minute secondary teeth ; subapical spines of moderate 

 length, smooth. Uropoda shorter than the telson, inner plate a little longer than the 

 outer. Lenofth 24 mm. 



Remarks. — I have felt some douljt in referring this form to the typical species, as 

 neither the very strong spine on the third caudal segment, nor the peculiar flattened 

 spine of the carapace, behind the rostrum, has been represented in the figure given in 



