coe: nemerteans of west and northwest coasts. 83 



IV. Heteronertxertea. Brain and lateral nerves imbedded in the 

 body musculature, which has three distinct layers, sometimes with an 

 additional layer of diagonal libers. Lateral nerves situated outside 

 circular muscular layer ; otherwise as in the Protonemertea. This 

 order corresponds to Hubrecht's Heteronemertea with the addition 

 of the Taeniosomidae. 



Although Burger's classification is an improvement over those 

 which have preceded it, yet I quite agree with Bergendal (: 00) that 

 the relationship of Carinoma with Carinella is so very striking 

 that their disposition in different orders is wholly unwarranted, and 

 now that the new genus Carixomella is described in the present 

 article the last objection to the union of those tAvo genera in 

 the same order is removed. For in Carixomella we have (as 

 described below) a form which presents many characters thought 

 to be peculiar to Carinella combined ^nth others so strikingly like 

 those of Carinoma that there was some hesitation as to which of 

 these two genera should receive the new species. The establish- 

 ment of the new genus Carinomella as a form intermediate in 

 character between Carixella and Carixoma appeared to be the 

 only reasonable procedure. The last barrier between the Protone- 

 mertea and the Mesonemertea is thus removed as far as Carinoma 

 is concerned. 



Whether the species of Cephalothrix should stand alone as 

 the representatives of the order Mesonemertea or whether they 

 should be again placed among the Protonemertea wiU depend u])on 

 further studies of the anatomical peculiarities of this somewhat 

 aberrant genus, whose nei)liridial system and some other points of 

 anatomy still remain unknown. The fact that there is no more 

 fundamental difference in the muscular layers nor in the position of 

 the lateral nerves than obtains in different portions of the body of 

 certain of the Carinellidae and in Carinoma would indicate that the 

 genus might be {placed with Cajkinoma and Carixomella in the 

 Protonemertea -wathout serioiis ol)jection. 



Such a disposition of Cephalothrix would do away with Bur- 

 ner's Mesonemertea and leave his three other orders. But the order 

 Protonemertea would thus become practically equivalent with 

 Hubrecht's order Paleonemertea lacking the Taeniosomidae, and 

 this order of Hubrecht's has therefore been adopted in the present 

 article. 



