302 



CRUSTACEA. 



of the shield, owing to which the bases of the eye-stalks appear to 

 be covered by the rostrum only. None of these features, taken 

 alone, is to be relied upon in distinguishing between the Alima 

 and the Urkhthus, since forms are known which, by the anterior 

 position of the mouth and the covering of all the thoracic segments 

 by the dorsal shield, show affinities with the Erickthus, while, by 



the uncovered condition 

 of the eye -stalks and 

 the flattening of the 

 cephalo - thorax, th e y 

 show Alima character- 

 istics. Such transition- 

 ary forms have been 

 called Alimerichthus. 



The youngest known 

 Alima stages (Fig. 144) 

 probably correspond to 

 the Pseudozoaea de- 

 scribed above in connec- 

 tion with the ErtchthuB 

 series. The anterior an- 

 tenna already shows the 

 rudiment of the acces- 

 sory flagellum, while in 

 the second antenna, 

 which ends in an oval 

 plate, the rudiment of 

 the flagellum is still 

 wanting. The first pair 

 of maxillipedes (I) are 

 long and palp-like, while 

 the second pair (II) have 

 already assumed their 

 final form as prehensile 

 organs. The three following pairs of maxillipedes (III-V) as well 

 as the three pairs of biramose ambulatory limbs are entirely wanting. 

 The tegmenta to which these latter belong may still be indistinctly 

 ) narked off. The four anterior pairs of pleopoda are well developed, 

 while the fifth and sixth abdominal segments are still but slightly 

 developed as limbless rudiments. It appears that the Alima 

 leaves the egg in the form just described (c/ P. Mayer, No. 138, 



l'u:. 144.— Youn- Alima larva (after Brooks), a', first 

 antenna ; a", second antenna ; /, II, first and second 

 maxillipedes; 0, 7, S, three posterior thoracic segments ; 



"' " :j , first live pleopoda. 



