EEPORT ON THE CEUSTACEA MAORTTRA. 243 



Nauplius with Penseus; either of these being demonstrated will prove the connection, and 

 establish the splendid hypothesis of Fritz Miiller. 



The recent discovery of Professor Brooks that the brephalos of Leucifer is a Nauplius, 

 brings the supposition in relation to Penseus within the range of probability. But as 

 the youngest form of Sergestes that has been observed is believed to be an Elaphocaris, 

 and this so early that the yolk-cells were still visible, and as Sergestes is nearer in 

 family relationship to Penseus than to Leucifer, I think it is advisable stUl to wait 

 before asserting that the young of Penseus is a Nauplius. 



Professor Brooks states 1 that having captured and kept in confinement a specimen, 

 he witnessed every moult between the youngest Protozoea and the young Penseus, and 

 that consequently all the metamorphoses of Penseus have been observed, and there is 

 no longer any ground for the attitude which certain over-cautious naturalists have 

 assumed in refusing to accept Fritz Mulder's conclusions untd more complete proof 

 should be furnished. 



Mr. Walter Faxon of Cambridge, Mass., 2 in commenting on Professor Brooks' researches, 

 says that the latter "has proved the connection between the stages older than the 

 Nauplius. That the Nauplius belongs to the same series he has not shown. In fact, 

 his youngest Protozoea is an older stage than the youngest stage secured by Fritz 

 Miiller. He has riveted the links in Miiller's chain that were closely joined before, but 

 has not touched the weak spot." Mr. Faxon further remarks that " The larval stages of 

 Penseidae seem to be not uncommon in the warm seas. Besides the published figures of 

 Miiller and Claus, I have seen the drawings of the developmental stages, from the 

 Protozoea onwards, made by Mr. Alexander Agassiz at the Tortugas Islands, in 1881, 

 and by Mr. J. W. Fewkes at the Bermudas in 1882. No observer has rediscovered 

 Miiller's Nauplius; yet in the light of our knowledge of the development of Mysis, 

 Euphausia and Leucifer, I see no good ground for refusing to accept Miiller's reason for 

 believing his Nauplius and Zoea stages to be parts of one life-history." 



Penseus canaliculatus, Olivier (PL XXXII. figs. 1, 2). 



Pensms canaliculatus, Olivier, Encycl. Method., vol. viii. p. 660. 



,, „ Milne-Edwards, Hist. Nat. Crust., torn. ii. p. 41 4. 



„ ,, Sp. B., Ann. and Mag. Nat. Hist., ser. 5, voL viii. p. 174, pi. xi., 1881. 



Rostrum slightly arched, furnished on the upper surface with nine teeth, the posterior 

 of which stands on the gastric region a little unequally distant from the preceding, and 

 one tooth on the lower margin, immediately below the most anterior of those on the 

 upper. Dorsal carina gradually lessening to near the posterior margin, channelled in 



1 Johns Hopkins University Circular, vol. ii., No. 19, p. 6, 1882. 



2 General Notes, Zoology U.S., Mas3., May 1883. 



