686 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXI. 



filament. In this condition the}^ could easily be mistaken for chalimi, 



and no doubt have been before now. 



From one small shark on July 4, 1904, a strip of skin an inch long- 



and half an inch wide, taken from just in front of the posterior dorsal 



fin, contained thirty-five of these embrj^os. 



On removing- them from 

 the shark's body and ex- 

 amining- them under mag- 

 nification they are found to 

 resemble a chalimus quite 

 closely in their structure 

 and in the number and ar- 

 langement of their ap- 

 pendages. The essential 

 points in which they differ 

 are the entire lack of a 

 frontal filament, which 

 materially alters the form 

 of the frontal plates and 

 the structure of the second 

 antenna\ In this bunch 

 of thirty-five were found 

 all stages of de\'elopment, 

 from a metanauplius just 

 attached up to larva? ready 

 to molt into the adult 

 form. 



The metanauplius (fig. 

 4) is quite similar to that 

 of CaJigus and' Lepeoph- 

 thelnis, so nearly hke 

 them as to be readily 

 recognized and yet so dif- 

 ferent that there can never 

 be any danger of confu- 

 sion. The carapace is 

 spindle-shaped, narrowed 

 both anteriorly and poste- 

 riorly, and consists of the 

 head fused with the first 



thoracic segment. This fusion is more complete than it was in the 



metanauplius of the Caliginfe, and con.stitutes a noticeable difference 



between the two subfamilies. 



In this particular, then, the Alehioii metanauplius is as far advanced 



as the chalimus of the Caliginse, and exhibits the first step toward 



0*5 mm. 



Fig. 4,— The meta.vauplius of Alebion glaber. 



