246 F. W. EDWARDS. 



all but the outer ones strongly trifid. About 100 rows of books in the anal sucker, 

 12 in a row. Gills simple. 



Pupa. — Respiratory tufts mucb shorter than the pupa, divided near the base into 

 four main branches, the two inner ones larger than the outer ones, each branch 

 again dividing two or three times into twigs, so that upwards of 60 filaments may be 

 counted. Cocoon, a dark matted mass of silk, of no definite form, secreted on the 

 rock, the pupae only partly covered. 



Distribution. — Mr. F. Jenkinson has shown me a specimen said to have been taken 

 at Crowborough, Sussex. Otherwise I have no records to add to those previously 

 given, which all referred to the Scottish highlands. 



17. S. tredecimatum, sp. nov. (figs. 2h, 4g). 



Adult. — Not yet recognised. 



Larva. — One of the largest, if not the largest, of the genus. Head markings of the 

 same type as in S. ornatum, but more diffused ; a dark dot in the region of the eyes, 

 and a pair about the middle of the clypeus. Antennae 4-jointed, the first two joints 

 membranous, pale, the last two dark ; first and third joints about equal in length, 

 second more than twice as long as either, fourth minute. Mentum with 11 divisions 

 apically ; except for the middle three these are so short and blunt that they can 

 hardly be called teeth ; the divisions are not noticeably trilobed. Sides of mentum 

 with about four long hairs. About 110 rows of hooks in the anal sucker, and about 

 18-23 hooks in each row. No ventral tubercles on last abdominal segment, but the 

 whole segment is much more swollen ventrally than in most species. Skin round 

 anus bare. Anal gills simple. 



One specimen was sufficiently developed to allow the pupal respiratory organs 

 to be dissected out ; these agreed closely with the pupa described below. 



Pupa. — Respiratory organ hardly more than a quarter as long as the pupa, 

 divided into thirteen filaments in all. At the base there are four main divisions ; the 

 first of these extends upwards nearly vertically for a short distance, emitting two 

 branches close together near its base and a little higher up dividing into three ; 

 the second divides into two close to its base ; the third and fourth each split into 

 three a little way from the base. No cocoon present in the material available. 



The above description has been drawn up from one pupa (evidently freshly formed) 

 and a number of larvae in the British Museum, bearing the label, " from stomach of 

 a trout, England." Most unfortunately no other data are available, but the species 

 is so very distinct in both larval and pupal stages that it seems worth while to 

 describe it, in order to call attention to the existence of such a remarkable form, even 

 though it may ultimately be discovered that there was an error of labelling, or that 

 the adult was already known under another name. There is a bare possibility that 

 the species may be S. hirtipes, the early stages of which, as mentioned above, have 

 not been described from Europe. However it seems very unlikely that two forms' 

 which are to all appearances identical in the adult stage (as are the American and 

 European races of S. hirtipes) should yet differ so widely as larvae and pupae. No 

 species has hitherto been described from any part of the world with 13-filamented 

 respiratory organs in the pupa. 



