nemerteans. 115 



Synopsis of the genus Drepanophorus. 



Since the publication of Burger's Monograph in 1895 several new species of Drepano- 

 phorus have been described. With the idea partly of assisting future workers and partly 

 of drawing attention to the gaps in our knowledge I have prepared the small table below 

 by selecting such features as seem likely to prove of use in classification. Since, as can 

 be seen from this table, the gaps in our knowledge are considerable, it is not yet possible 

 to arrange the existing species in any order expressing their relationships. Roughly it 

 may be said that the majority of the genus conform to a certain type of which D. crassus 

 may be taken as the example. More or less closely resembling this species are the European 

 I), igneus and D. albolineatus, together with the exotic forms D. latus, D. lifuensis, and 

 D. roseus. The remaining species are, so far as can be seen, more widely separated from 

 one another. The enormous development of the glandular portion of the cerebral organ 

 characterises D. cerinus and, to a lesser degree, D. willeyanus. D. lankesteri is conspicuous 

 by the ventral position of the gonidial pores, the fusion of the anterior rhynchocoelomic 

 pockets, and the regularity of its ventral nerve commissures. Perhaps the form, which diffei's 

 most from the rest, is D. borealis, the only Arctic species known. In its broad, stumpy 

 body, the ventral openings of the cerebral organ, the dorsal position of the gonidial pores, 

 the small number of eyes, and the peculiar expansions of the rhynchocoelom over the brain 

 it stands apart from the remaining species. 



In order to include the more recent species the diagnosis of the genus below shews 

 a few points of difference from that given by Burger, though these are by no means 

 numerous or very important. 



Genus Drepanophorus. 



Flattened forms exhibiting a relatively great breadth in comparison to their length. 



The mouth and rhjmchodaeum open separately. The proboscis is large and contains 

 14 — 32 nerves. Its armature is characteristic for the genus. 



The proboscis sheath gives off lateral diverticula alternating regularly with the gut 

 pockets. 



The nervous stems are ventral in position and the distance between them is seldom 

 more than half the diameter of the body laterally. They unite posteriorlj^ above the 

 anus. 



The cerebral organ is large and never lies in front of the brand. 



Small longitudinal head furrows (" Kopfgrubchen ") are developed in connection with the 

 circular head furrow. 



Neurochord cells occur in the ventral ganglia. 



The eyes may be few or numerous but are always of large size. 



Head glands but slightly developed. 



The sexes are separate. The gonads exhibit great divergence in the number and 

 position of their ducts. 



15—2 



