216 ON NEREIS SUCCINEA AND PERRIERI. 



kindness. For, my specimens in some regards (length of the 

 tentacular-cirri and shape of the posterior parapodia) deviate 

 from the description given by Ehlers, and moreover I was 

 struck by the great resemblance of the Zuiderzee-worms 

 with the Nereis Perrieri St. Jos. from the Coast of France 1 ). 

 Nereis succinea as well as N. Perrieri is characterized by 

 the leaf-like development of the dorsal ligule with the 

 parapodia of the posterior segments and the close affinity 

 of both species was already recognized by de Saint-Joseph 

 himself 2 ); however N. succinea differs from the last-named 

 species by having shorter tentacular cirri, more teeth at 

 the mandibles and a smaller number of segments. The 

 Norderney-specimen of Nereis succinea from the Göttinger 

 Museum, that shows an indifferent state of preservation, is 

 a rather stout worm, measuring 80 mm. in length, 6 mm. 

 in its greatest breadth (with parapodia) and has only 68 

 segments. The length, stated by Leuckart for this species, 

 is 100 to 150 mm., but unfortunately he does not mention 

 the number of the segments. All the specimens from the 

 Zuiderzee are much smaller, the largest of them measuring 

 hardly 50 mm. in length and 5*/ 2 nim. in breadth ; however 

 the number of their segments amounts to about 100. Taking 

 this in account and also the well-known fact, that among 

 the individuals of an Annelid there often reigns a great 

 disagreement in the number of segments, I believe that the 

 small number of segments of the Norderney-worm has to 

 be considered as an exception. A character of more im- 

 portance to distinguish N. succinea from N. Perrieri appears 

 to be the different length of the tentacular cirri, for in the 

 Norderney-specimen these cirri, reversed, do not extend 

 farther backward than to the 4 th segment, as already stated 

 by Ehlers. 



In N. Perrieri however the longest tentacular cirri extend 

 till the 7 th setigerous segment, therefore four segments more 

 backward. Now our Zuiderzee-specimens show great difie- 



1) Ann. d. Scicnc. natur. Zoölogie, 8e Sér. t. V, 1898, p. 288, pi. XV, 

 figs. 69—77. 2) loc. cit. p. 292. 



Notes from the Leyden Museum, Vol. XXX. 



