66 



a much more cylindrical body with large deep furrows between the 

 segments, and in having the fixed caudal segments very short. 



The genus Gracilaria is undoubtedly the most generalized, if we 

 consider the peculiar structures (Fig. 47) found in some species to 

 be maxillary palpi. The tendency in the Gracilariidae is toward the 

 loss of the maxillary palpi, and the development of the triangular 

 type of prothorax, which usually is elevated on the median line. There 

 is also a shortening of the maxillae and labial palpi and of all the ap- 

 pendages in relation to the rest of the body, and a stronger chitiniza- 

 tion of the surface of the body tending to a soldering down of the 

 appendages. There is also taking place the development of two sizes 

 of spines on the dorsum of the abdominal segments and the formation 

 of single rows of larger spines. Finally there is the development of 

 the cremaster. There are two distinct divisions of the Gracilariidae 

 to which subfamily names have been given. These may be separated 

 as follows : 



a. Prothorax depressed' and neck-like, somewhat quadrangiilar in out- 

 line, the length at the lateral margin never more than twice the 



mesal length Gracilariinae. 



aa. Prothorax usually with an elevated ridge on the meson, triangular 

 in outline, the length at the lateral margin about four times the 

 mesal length Lithocolletinae. 



Subfamily Gracilariinae 



The Gracilariinae (Figs. 45 and 46) include all the genera in 

 which the generalized quadrangular type of prothorax has been re- 

 tained. In all the genera the caudal end of the body is blunt and the 

 tenth segment bears a row of 6 or 8 spines, larger than those on the 

 other body segments. The labial palpi are always long and never 

 covered by the maxillae at their proximal end. The following table 

 will serve to separate the genera of Gracilariinae : 



a. Dorsum of abdomen sparsely covered with very coarse spines, some- 

 times with additional fine spines. 

 b. Head with a cutting plate on the ventral surface near the cephalic 

 margin, which is usually serrate ; maxillae as long as the mesotho- 



racic legs Gracilaria Haworth. 



bb. Head with a prominent projection at the cephalic end, not a 

 distinct plate; maxillae never as long as the mesothoracic legs. 



Ornix Treitschke. 



aa. Dorsum of abdomen thickly covered with very fine spines which are 



almost invisible Parectopa Clemens. 



