66 THE NAUTILUS. 



mania, 1878, p. 24) : " In the young state the shell is simple and re- 

 sembles the common Ancylus in the same neighborhood." 



From the fact that Ancylus it'oodsii (op. cit. p. 23) is omitted by 

 its author from his last catalogue (op. cit. 1890, p. 145) I infer that 

 he now considers that name to be a synonym, and further that he 

 considers it a synonym of G. pelterdi. If so, it is a matter for re- 

 gret that Mr. Johnston has withdrawn his species in a manner to 

 confuse a student of his writings. 



The published figures of the juvenile shell only represent the 

 stage at which the septum is completed and the secondary growth 

 is about to occur. Thanks to a series of specimens collected by 

 Mr. Suter in New Zealand, which probably represent the fry of an 

 undescribed species, I am enabled to detail the process. My friend 

 supposes that in unfavorable circumstances a septum is never 

 formed, a view which his American experience had already sug- 

 gested to Gibbons. If this be the case, and Gundlachia sometimes 

 continues to regularly enlarge the ancyliform shell, then only an 

 anatomical examination could distinguish between the genera; and, 

 although several supposed species have been named, and more or 

 less adequately described as Australian, yet this hypothesis would 

 require proof of the existence of Ancylus in Australia. 



The first deviation shown by young Gundlachia from Anc>/fn.t 

 consists of a fold appearing at the posterior end of the aperture. 

 No increase occurs round the rim of the aucyliform shell until 

 the fold is built into a septum flooring half or two-thirds of the 

 original shell. This septum is flat and grows asymmetrically, the 

 right margin advancing before the left. At this stage the shell 

 has much resemblance to a spectacle-case, aud has been well figured 

 by Pfeifler. Vigorous growth now occurs; in front, but in an 

 altered plane, the margin of the ancyliform shell is continued out- 

 wards, behind, the shell is spread beneath the septum floor to form 

 the roof of the secondary shell, then leaving the septum it is ab- 

 ruptly bent downwards. A slight inclination to' spiral growth is 

 shown by the increase on the right exceeding that on the left 



Stimpson suggests " that the Gundlachia commences its life as an 

 Ancylu*. ... it passes the first summer and autumn of its 

 existence in this smaller shell, and that the septum, which afterwards 

 partially closes its aperture, is formed during the period of inaction 

 which ensues during the winter. This septum would, in some de- 

 gree, serve as a protection to the mollusc during this period, in the 



