DESCRIPTIONS OF GENERA AND SPECIES 



561 



Another possibly diagnostic character of the genus (as contrasted, of course, with 

 other Acanthodrilids) is apparent in the figures of Michaelsen. The spermatheca 

 is divided by a sharp constriction, below which arises the single diverticulum (when 

 there is only one). The shape is very characteristic. In two species Michaelsen (16) 

 has described structures which look like spermaphores protruding from or lying within 

 the pouches. Possibly, too, the development of muscular fibres round the end of the 

 sperm-duct is a character of importance in distinguishing Benhamia. I have found 

 it in B. crassa and B. holavi. Unfortunately, too few species of the genus have 

 been investigated histologically to allow of putting this forward as more than 

 a suggestion; it is a point of resemblance to the genus Microdrilus and to Ocnero- 

 drilus among the Cryptodrilidae (see p. 511). So, too, is the dorsal diverticulum 

 of the b\iccal cavity (see p. 458), which is, perhaps, so far as this family is con- 

 cerned, distinctive of the genus Benhamia. The other generic characters are embodied 

 in the above diagnosis, and have been, to some extent, already discussed (see p. S^S)- 



The species of this genus are not by any means easy to distinguish ; they differ 

 in very small characters. And, in addition to this, the difficulties are increased 

 by the fact that a good many of them are but imperfectly known. The genus 

 itself, on the other hand, seems to be capable of being very easily defined ; this, 

 indeed, is the difliculty when we come to the species ; all the characters which 

 vary much in other Acanthodrilids are fixed as generic characters. Some of the 

 very smallest Acanthodrilidae belong to this genus, and, on the other hand, two 

 of the largest of earthworms, B. rosea, and B. itoliensis. 



The table on the preceding page will enable the species to be roughly grouped ; it 

 embodies the principal differences which exist between the species, not taking into 

 consideration those which characterize only a single species, such as, for example, the 

 accessory copulatory organs of B. beddardi. 



The above thirty-one species are all that are at present known as belonging to 

 the genus ; but it is not certain that they are all ' good ' species. 



The Table will enable the species to be roughly sorted for purposes of identifi- 

 cation into the following groups : — 



Small sized species, with anteriorly placed first dorsal pore and with ornamented 

 penial setae. 



B. annae. B. sylvestris. 



B. floresiana. B. castanea. 



B. crassa. B. curta. 



B. whytei. B. parva. 

 B. mouticola. 



4C 



