236 



F. W. EDWARDS. 



References. — ^It is possible that S. argenteostriata, Strobl, as described by Corti 

 (Atti Soc. Ital. Sci. Nat. liii., p. 192, and liv, p. 223, 1914-16) is the spring form of 

 this species, but I have not seen Italian specimens. The pupal filaments have 

 recently been figured by Friederichs (Zeitschr. f. angew. Ent. vi, p. 61, 1919). 



10. S. equinum (L.) Edw. (figs, li, 2d, 3c, 6a, b & c). 



Larva. — General colour rather bright green, body-markings darker green, but 

 not conspicuous. Head with 6 distinct dark spots, 4 arranged as usual in the form 

 of a cross, the other two being on the posterior margin of the clypeus. No dark 

 stripe above the eyes. Antennae rather slender, 4- jointed ; the second joint nearly 

 twice as long as the first or the third, which are about equal in length ; fourth minute. 

 Mentum with 9 simple teeth in the terminal row, the central one and the one at 

 each end much larger than the others. About 100 rows in the anal sucker, each with 

 20-25 hooks. No ventral papillae on last segment. Skin round anus bare. Anal 

 gills simple. 



Fig. 6. SimuUum equinum, L. : a, pupal skin of a hatched specimen 



projecting from mouth of cocoon, X 10 ; b, respiratory organ of left side, 



seen from the right, X 25 ; c, variety of pupal respiratory organ, X 25, from 



a specimen found in the River Test by Mr. M. E. Mosely. 



Pupa. — Respiratory organs consisting of thick tubes instead of long thin filaments. 

 Close to the body of the pupa the organ divides into a dorsal and a ventral section, 

 which are entirely in contact with the pupa on the one side and with the cocoon on 

 the other. The tips of these dorsal and ventral sections are abruptly narrowed and 

 slightly overlap those of their fellows of the opposite side. From the dorsal section 

 there project forwards five rather short and stout branches, two on the outer side 

 and three on the inner ; the ventral section gives off a single branch near its base ; 

 these branches are not more than one-third of the length of the pupa. Including the 

 tips of the main sections, there are thus eight branches in all. The chitin forming 

 the tubes is very thin and usually bears minute spines scattered over its whole 

 surface, visible as dark dots under a magnification of 100. Cocoon closely woven, 

 somewhat boot-shaped, that is to say, the anterior part of the floor is raised at an 

 angle with the remainder, the opening being practically circular ; anterior margin 

 not thickened. 



