ON NEREIS SUCCINEA AND PERKIERI. 



217 



rences in that respect, for in some of thera the longest 

 tentacular circi reach the 8 th , even the 9 th segment, whereas 

 in others, from the same locality, they do not extend farther 

 backwards than to the 5 th segment or the anterior border of 

 the 6 th one. Therefore, in my opinion, there cannot be 

 assigned a great systematical value to this character. Lastly 

 only remains the different number of teeth in the maxillae 

 of both species, for in N. Perrieri there are only 4 to 5 

 of them, whereas the jaws of N. succinea possess 8 to 9 

 teeth. Though the maxillae of the Norderney-specimen have 

 the teeth not very distinctly separated, and hardly 6 or 7 

 of them can be recognized, all our Zuiderzee-worms show a 

 great number (8 to 9) of distinct teeth. The question there- 

 fore remains, whether in all specimens of N. Perrieri the 

 teeth of the jaws are so less developed, as described by de 

 Saint-Joseph. On the contrary I observed a remarkable 

 agreement in the arrangement of the paragnathi of the 

 proboscis of both species ; for in N. Perrieri, as stated by 

 de Saint-Joseph, both lateral groups upon the dorsal side 

 of the basal region of the proboscis (VI) consist of a circle 

 of 6 to 7 small paragnathi around a large cen- 

 tral one. Now this character is also very distinct in the 

 Norderney-specimen and is also visible in most of the 

 Zuiderzee-worms. Upon the dorsal median area (V) there 

 are usually two paragnathi, obliquely placed next to each 

 other. As for the paragnathi of the maxillary region in the 

 Norderney-specimen, group I contains 3 of them, placed 

 behind each other, quite like in N. Perrieri; however in 

 some of our Zuiderzee-specimens this number amounts to 6. 



With regard to the shape of the superior ligule in the 

 parapodia of the posterior segments, perhaps it could be 

 concluded from the figures of Ehlers (pi. XXII, fig. 21), 

 that with N. succinea this lobe is more developed in a 

 horizontal direction and that the dorsal cirrus is hardly ex- 

 tending beyond the tip of the ligule. However I believe, 

 that the imperfectness of this figure must be ascribed to 

 the rather indifferent state of preservation of the worm ; 



Notes from the Ley den Museum, Vol. XXX. 



14** 



