THE NAUTILUS. 115 



gill hardly narrower anteriorly, its anterior insertion broad, occupy- 

 ing the whole space between the anterior end of the outer gill and 

 the posterior end of the palpi (the ascending part of the mantle- 

 attachment line); the inner gill is in direct continuation of and in 

 contact with the inner palpus, in fact the base of the latter is actually 

 connected with the inner gill for a short distance. 



Outer lamina of outer gill entirely connected with the mantle; 

 inner lamina of inner gill entirely connected with abdominal sac; 

 posteriorly to the foot the two inner laminae are connected with each 

 other as usual, thus forming the diaphragm, but the four gills do not 

 extend as far back as to the posterior mantle margin, and the poste- 

 rior part of the diaphragm is formed by the union of the two mantle 

 edges, which form a solid bridge (d in the figure 6 on pi. ii). The 

 latter is 4 mm. long, while the gill part of the diaphragm is 16 mm. 

 long (in a specimen of which the total length of the soft parts is 

 about 82 mm. 



A male not being present, the structure of the gills cannot be made 

 out, but it very likely is identical with the structure of the outer gill 

 in the female. 



In the female the inner gill serves as marsupium, but only the 

 inner portion of it, about one-fourth of its length at the anterior end 

 and a little less than one-fourth at the posterior end, being non- 

 marsupial. The swelling of the marsupium during the breeding sea- 

 son is not very great, and its edge remains sharp. 



In the non-marsupial outer gill a development of septa and water 

 tubes is barely indicated, in fact there are none, as compared with 

 North American forms. There are rather slight, indistinct and dis- 

 tant ridges running on the inner side of the laminse from base to edge, 

 parallel to the direction of the filaments, but these ridges are not 

 connected with each other across the interlamellar cavity, except at 

 certain points by more or less cylindrical connections. The latter 

 are more distinct and frequent and stronger near the base of the 

 gill; they are rather scarce and slight in the middle of the gill, and 

 again better developed toward the edge, where they sometimes are 

 slighly elongated and like septa. But there are no continuous septa 

 whatever, and thus the interlamellar space is not divided into water 

 tubes. 



In the marsupial part of the inner gill the connections between 

 the two laminae are more crowded and numerous and become more 



