DOLICHOBHYNCHUS INDICUS, A NEW ACEANIATE. 269 



Dolichorhynchus indicus, n. g., n. sp. 

 A New Acraniate. 



By 

 Artliiir Willey. 



In the collection of Polyclijeta made during the voyages of 

 H.M.S. ^'' Investigator/' in the Indian Ocean, under the 

 direction of Dr. Alcock, there is a tube containing several 

 specimens of an Amphioxus, which on inspection has 

 proved to be the type of a new sub-genus of the genus Bran- 

 chiostoma. 



Not one of the specimens appears to be in a condition of 

 sexual maturity, in spite of the fact that the largest attains a 

 length of 25* 75 mm. The body is elongated, slender, late- 

 rally compressed, and tapering gradually towards the posterior 

 end. There are seventy-one, myotomes, and the formula is 

 42-14—15. 



The feature which at once differentiates it from all other 

 known forms of Amphioxus is the great length of the proe- 

 oral lobe, close upon 2 mm. measured from the anterior 

 termination of the neurochord, or equal in length to the first 

 six myotomes (Fig. 1). The metapleural folds terminate sym- 

 metrically some distance behind the atriopore on either side 

 of the ventral fin, a fact which denotes the systematic posi- 

 tion of the species in the absence of data afforded by the 

 gonads (Fig. 2). There are about forty-five ventral fin cham- 

 bers behind the termination of the metapleural folds, and 

 four or five in front of this point. In the specimen figured 

 the tentacular cirri (buccal cirri) are mostly concealed witbin 

 the vestibule of the mouth, but the ends of several are pro- 

 jecting from beneath the oral hood in front. 



The dorsal fin is well marked, being about one fifth the 



