DESCRIPTIONS OF GENERA AND SPECIES 



023 



The Geoscolicidae form a family which is easily to be defined; very few of tho 

 characteristic features of the group are to be seen in other worms. There is, 

 however, no one character found in all the Geoscolicidae, which is absolutely 

 distinctive of the family. The definition given above shows a collection of characters 

 which are nowhere else met with. The characters which are found in all the 

 Geoscolicidae without exception are the following: 



(i) Setae not more than eight in a segment 1 . 



(z) Nephridia never diffuse, always paired (two pairs in Bnwhydrilus). 



(3) Spermatheca without diverticula. 



(4) Gizzard (or gizzards) in middle of oesophagus. 



These four characters could not be applied to any other family ; the Eudrilidae 

 and Lumbricidae are only just out; the former by reason of (2), the latter of (4). In 

 the following list are characters found in a large number of genera (the number 

 indicated in brackets), but sometimes not unknown outside the group. 



(1) Setae ornamented (9). This occurs only in Deodrilus, and rarely 



in Perionyx. 



(2) Clitellar setae differentiated in some Lumbricus, Allolobophora, Allurus. 



way (nearly all Geoscolicids). 



(3) First nephridium modified to form This is found in Acanthodrilus, Octochaetus, 



a large gland, which sometimes opens 

 into buccal cavity. 



and in connexion with buccal cavity 

 in other Megascolicids with diffuse 

 nephridia; also in Lybiodrilvx, 



(4) Nephridia commonly specialized into 



two series, those of anterior segments 

 being different in some particular 

 from those which follow. 



(5) Setae irregular in arrangement (4). In tail region of a few Cryptodrilids. 



(6) Setae defective on a few anterior seg- This is seen in Deodrilus. 



ments (8). 



(7) Sperm-sacs long, extending through Found also in Typhaeus and in Polyto- 



Beveral segments (4). reutus. 



(8) Spermathecae far back, in neighbour- This occurs in all Eudrilids, and is cha- 



hood of gonads (8). racteristic of Lumbricidae. 



I discuss the affinities of the family under Lumbricidae and Eudrilidae (qq. v.). 

 1 The occasional occurrence in Onychochaeta of nine setae is not perhaps a constant exception. 



