MUSEUM OF COMPARATIVE ZOOLOGY. 153 



resembles that of A. Gouldiana. There is no jaw, nor any radula, so this fea- 

 ture may be taken as diagnostic of Aurinia. There are two little cartilaginous 

 pads near the tip of the proboscis. There is no opercular pad or operculum, 

 nor was there any visible color gland. 



On the whole, the general characters of the soft parts agree well with 

 A. Gouldiana, though differing in some minor details. 



Aurinia robusta n. s. 



Plate XXXV. Fig. 2. 



Shell large, stout, with a chalky external layer under a thin pale yellow epi- 

 dermis, and an internal porcellanous white layer ; a strongly curved and re- 

 curved canal ; four columella plaits, nearly obsolete in the adult; the surface 

 finely spirally striated; earlier whorls with the suture appressed and numerous 

 (on the fourth whorl about 25) small short transverse riblets mounted on the 

 periphery ; outer lip sharp ; throat pure white ; pillar lip merely glazed, ex- 

 terior spotted with squarish brown spots with less regularity of size and posi- 

 tion and more distant than in S. junonia ; whorls six beside the nucleus, fully 

 rounded, somewhat irregularly coiled. Lon. of shell, 119.0; of last whorl, 

 100.0 ; of aperture, 8S.0 mm. Max. diameter of shell, 52.0 mm. 



Nucleus small, of , one and a half concave whorls, with the acute initial point 

 central, rising above the margin of the concave, which is formed by the sharp 

 posterior edge of the first post-embryonic whorl ; this whorl is sculptured 

 with very low flat striated transverse riblets with narrower channelled inter- 

 spaces, extending clear across the whorl and both crossed by about eight dis- 

 tinct spiral threads between the two sutures ; after the first turn the transverse 

 bands become narrower, the interspaces about equal to them, and he spiral 

 threads wider and flattened so that a fine and exceedingly elegant trellising is 

 the result. The second whorl begins to be spotted with squarish brown spots 

 with fainter edges, of which seven series appear at the end of the second turn ; 

 interior yellowish white with four sharp plaits on the pillar, very oblique, and 

 growing stronger backward ; epidermis smooth, thin, not polished ; suture 

 very closely appressed. Lon. of this young shell, with nucleus and two whorls 

 12.0 ; of second whorl, 11.0 ; max. diarn., 5.0 mm. 



Habitat. Station 55, off Havana, in lat. 22° 9' .5 and lon. 82° 21'.5, in 242 

 fms.; Station 50, lat. 26° 31' and lon. 85° 53', in 119 fms ; U. S. Fish Com- 

 mission Station 2397, in the Gulf of Mexico, lat. 28° 42', lon. 8G° 36', in 

 280 fms., gray mud, bottom temperature 40°. 1 F. 



This fine and remarkable species is peculiarly distinguished by its chalky 

 outer layer, under a pale epidermis, which becomes eroded, like that of a fresh- 

 water shell. The form of the nucleus, if the hypothesis of a membranous em- 

 bryonic first shell be admitted, would be due to a calcification which did not 

 extend to the dome of the membrane, while the acute initial point of the cal- 

 cified part may be supposed to occupy the vicinity of the pillar in the soft 



