244 FULIiETTN 181, UNTTEiD SIT'ATEe ISDATUOOS^AL MUSEUM 



This species agrees with A. (A.) fultoni in having the base rather 

 strongly axially ribbed, but it differs from it in having a much smaller 

 aperture. 



APEROSTOMA (APEROSTOMA) LAXATUM (Sowerby) 



Plate 35, Figuee 13 



1850. Cyclostoma laxatum Sowebby, Thesaurus Conchyliorum, vol. 1, Suppl. 



p. 159*, pi. 31A, fig. 302. 

 1852. Cyclotus laxatus Pfeiffer, Monographia pneumonopomorum viventium, 



vol. 1, p. 18. 

 1897. Neocyclotus (Neocyclotus) laxatus Kobelt and Mollendoeff, Nachrb. 



deutschen malak. Ges., vol. 29, p. 137. 

 1923. Poteria (Neocyclotus) laxatum H. B. Bakeb, Occ. Pap., Mus. Zool. Univ. 



Michigan, No. 137, p. 41. 



Although CyclostOTna laxatum Sowerby has been quoted by many 

 malacologists, we regret to say that we have none in the National 

 Museum collection that agree with Sowerby's description, figure, and 

 habitat ; we must therefore quote Sowerby's description and copy his 

 figure. His figure measures : Height, 18.5 mm. ; greater diameter, 36.4 

 mm. Height of aperture, 13.1 mm. ; diameter, 16.9 mm. 



"Shell of a depressed orbicular form, whitish, covered with a thick 

 orange-brown epidermis; spire depressed, with a rufous apex; volu- 

 tions four, rounded, covered not only with distinct lines of growth, but 

 also with irregular rugulosities, with two narrow zones, the posterior 

 white, the other fuscous, in front of which the epidermis is more 

 darkly coloured; aperture not quite circular, but very slightly ellip- 

 tical, and with a slight angle posteriorly close to the last volution; 

 peritreme tliin, anteriorly very slightly reflected; umbilicus very 

 large, showing internally the four volutions. 



"The shell is somewhat diaphanous, so that the white and dark- 

 brown zones are distinctly seen within the aperture. 



"Columbia. Mus. CumingP 



THE GROUP OF APEROSTOMA (APEROSTOMA) BLANCHETIANUM 

 Shell decidedly depressed. 



APEROSTOMA (APEROSTOMA) BLANCHETIANUM (Moricand) 



Plate 35, Figuees 7-9 



1826. Cyclostoma blanehetiavum Mobicand, Mem. Soc. Geneve, vol. 7, p. 442, 



pi. 2, figs. 21-23. 

 1847. Aperostoma blanchetianum Teoschel, Zeitsch. Malak., p. 44. 

 1847. Aperostoma ilanchetianum Pfh3:ffee, Zeitsch. Malak., p. 104. 

 1850. Cyclotus inca (pars) Gray, Nomenclature of molluscous animals and 

 shells in the collection of the British Museum, pt. 1, p. 6. 



