ATLANT. DEEP-SEA EXPED. 1910. VOL. 111.1 



HETEROPODA 



4) The presence or absence of peribuccal teeth, 

 irregularly grouped round the edge of the mouth, 

 in front of the two rows of buccal teeth always pre- 

 sent in the palate. 



5) The position of the pedal ganglion in correlation 

 to the anterior edge of the fin. As is well known, 

 this ganglion, which may be clearly seen without 

 dissection through the transparent cuticular wall, is 



placed at a considerable distance from the head, near 

 the base of the swimming fin. Its position seems 

 absolutely fixed in each species. In many species it 

 occupies the same position, viz: right above the 

 anterior border of the swimming fin, but in some 

 species it is placed more posteriorly, above the an- 

 terior third of the swimming fin. 

 6) The position and surroundings of the osph radium 



a 



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Textfig. A. 



1 a-b P. gegenbauri. 2 a-b P. hippocampus war. apunctata. 3 a-b P. hippocampus, var. punctata. 4 a-b P. minuta. 5 a-b P. coronata. 



This character, little used by earlier investigators, has 

 proved to be a very good specific mark. The long 

 linear osphradium is distinctly conspicuous, lying 

 anterior to the nucleus, surrounded in some way or 

 other by a cuticular wall. Its shape and position 

 seem to be quite constant in each species, and at 

 the same time differ from one species to another: 

 the osphradium may in one species be placed in the 

 median dorsal line, while in another it is placed on the 

 left side of the animal; the cuticular wall surrounding 

 the osphradium may, according to the position of the 

 latter, rise above the level of the body, or perhaps 



form a pocket-like structure on the left side above 

 the heart; it may be smooth or tuberculated. 



7) The arrangement, number and length of the gills. 



8) The tail also gives a number of characteristic 

 features of specific value: the number and width of 

 its longitudinal muscle bands, and the structure of 

 the cutis above these muscles. The latter may be 

 smooth or tuberculated, or it may be swollen so as 

 to form longitudinal ridges, especially along the dorsal 

 and ventral sides of the tail. 



A structure of specific value is also to be seen 

 in the horizontally extended fin at the posterior 



