8 



MONOGRAPH OF THE ATLANTI DAE. 



Atlantic, at least on account of the nautiloid shell, and 

 the keel extending to the outer lip of the aperture. Unfor- 

 tunately only a surface view of the shell is given (copied 

 by me, PI. I, fig. 44). I think the remarkable row of 

 » square, violaceous spots, following around the middle 

 of the spire" may be due to some accidental disposition 

 of the organs of the animal itself, and not inherent to the 

 shell. The diameter (nearly 6,5 mm.) also affords some 

 argument to the affinity to Oxygyrus, as this diameter 

 among the species of Atlanta is only attained by A. peroni, 

 from which *A. tessellata" must be certainly separated. 

 Some more certainty, however, cannot be obtained until 

 renewed investigation of the type-specimen. 



Finally » Atlanta mediterrariea" Costa, from the Mediter- 

 ranean, (copied by me, PI. I, fig. 41), which is most 

 imperfectly known, and which I had formerly (p. 10), 

 though hesitatingly, referred to Atlanta lesucuri, belongs 

 perhaps also in the genus Oxygyrus. 



Protatlanta mihi. 



1852. Atlanta {p.p.) Souleyet. 

 1862. Oxygyrus (p.p.) Macdonald. 



Shell cartilaginous (see note p. 3), spire short, conical' 

 projecting on one side, whorls much rounded in transverse 

 section; keel horny, very high, commencing most conspi- 

 cuously at the outer lip of the aperture, as in Oxygyrus, 

 and here, as in this last-named genus, consisting of two 

 plates, which leave a small space between them, in which 

 the mantle of the animal projects. 



Animal almost entirely as in Oxygyrus, with a very 

 bulky proboscis and short tentacles; sucker at the fin 

 very large. 



Operculum as in Atlanta, with a small spiral portion. 



The type of this new genus is » Atlanta lamanoni" of 

 Souleyet, which name has been altered by E. A. Smith 

 in » Atlanta souleyeti", as the term, used by Souleyet, had 



Notes from the Leyden Museum, Vol. XXX. 



