NOTES ON AMPHITRETUS. 



101 



On the other band, it seems to us that a very much nearer ally is 

 given in Alloposus, especially in A. pacificus. This species has in 

 common with Ampliitretus not only the similarly arranged suckers (see 

 foot-note on p. 87) and the very extensive webs, but also many other 

 points of fundamental importance as regards the histology and anatomy, 

 to which attention has already been called. It may almost be said that, 

 so far as is known, the only and the most essential distinctive character 

 between the two genera, Ampliitretus and Alloposus, consists in the 

 presence of the ventro-median connection of the mantle with the siphon 

 in the former. 



Verrill (/. c), in diagnosing the family Alloposidoa and the genus 

 Alloposus, has given that the mantle-edge is directly united to the head 

 by " a median-ventral and two lateral longitudinal commissures," in 

 addition to a large dorsal nuchal band. Prom this one might be led to 

 think that the " commissures," here spoken of, may be something 

 morphologically related to the ventro-median connection seen in 

 Ampliitretus. They may perhaps be considered as a forerunner of that 

 connection in so far only as they serve to bring close together the free 

 mantle-edge and the siphon-base ; but the " commissures " themselves 

 are, in our opinion, nothing peculiar to Alloposus (see foot-note on p. 87) 

 In fact, the ventro-median connection of Ampliitretus is totally un 

 represented in Alloposus as in any other Cephalopod genera. Since now 

 the " commissures " referred to forms the chief point in the characters 

 of the family Alloposidas of Verrill, it may be questioned if that family 

 can be held up as distinct from either the Philonexidoe or the Octopodidae, 

 to both of which it seems to show affinities in certain respects. 



Be that as it may, we agree with Hoyle in regarding Ampliitretus 

 as a representative of a distinct family, the Amphitretidae. As already 

 indicated, this family probably has its nearest ally in the genus Alloposus. 

 In the next place, it seems to us the family is more nearly related to 

 the Octopodidse than to any other family of the eight armed Dibranchiata, 

 as shown in its organization. 



