238 BULLETIQSr 181, UTSTTE© SfTATElS N!ATEO!N\A!L MUSEfDM 



1843. Cyclostomu giganteum Sowerby, Proc. Zool. Soc. London, 1843, p. 30. 



1847. Aperostoma giganteum Pfeiffeb, Zeitsch. Malak., p. 104. 



1850. Cyclotus giganteus Gray, Nomenclature of molluscous animals and shells 



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

 1897. Neocyclotus (Neocyclotus) giganteus Kobelt and Mollendorff, Nachrbl. 



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

 1901. Aperostoma giganteum Sykes, Journ. Malac, vol. 8, p. 105, pi. 10, fig. 1. 

 1923. Poteria (Neocyclotus) gignntea H. B. Bakeb, Occ. pap. Mus. Zool. Univ. 



Michigan, No. 137, pp. 40, 42. 



Shell gigantic, depressed-helicoid. The early whorls pinkish; the 

 later pale yellow, varying from yellow to pale chestnut, with a light 

 zone below the summit and a broader yellowish zone immediately 

 above the periphery. Tlie posterior half of the base is chestnut- 

 brown, while the anterior half and umbilical wall are yellowish horn 

 colored ; interior of aperture bluish. The nucleus consists of 2 very 

 small, well-rounded, smooth turns. The postnuclear whorls are 

 moderately rounded and appressed at the summit with an impressed 

 groove immediately below the summit. The postnuclear whorls are 

 marked by regular, retractively curved, closely spaced axial riblets, 

 which are a little wider than the spaces that separate them. On the 

 last half of the last whorl they become obsolete and are replaced by 

 mere lines of growth. Suture strongly impressed. Periphery well 

 rounded. Base with a very large open umbilicus, inflated, and 

 marked by the continuation of the axial ribs, which become fused on 

 the anterior half of the base and quite strong and well differentiated 

 into strong ribs on the umbilical wall. Aperture oblique, subcircular, 

 drawn into an obtuse angle at the posterior angle, which has a median 

 groove; peristome simple; that of the outer lip sharp and slightly 

 reflected, while the inner lip is thickened. The parietal wall is cov- 

 ered by a thick callus, which renders the peritreme complete. In the 

 peristome there is a shallow sinus at the posterior termination of the 

 columella. Operculum typically aperostomid, having 9 whorls. 



The specimen described and figured is one of two, U.S.N.M. No. 

 251101, collected by H. Pittier on the Cerro de Garagara, Panama, at 

 20 to 900 meters. It has 3.7 whorls remaining and measures : Height, 

 32.6 mm.; greater diameter, 56.7 mm.; lesser diameter, 38.3 mm. 

 Height of aperture, 23.5 mm. ; diameter, 27 mm. 



The depressed-helicoid form and gigantic dimensions readily dis- 

 tinguish this from the other members of the giganteum group. 



Reeve, loc. cit., p. 97, states: "Mr. Sowerby has kindly permitted 

 us to refer to his figure of Cyclostomata in part 2 of his Species Con- 

 chyliorum, which we are happy to announce is now nearly ready for 

 publication." This work, it would appear, was never published. 

 Gyclostoma giganteum Sowerby must be considered a manuscript 

 name, and the name Gyclostoma giganteum must date from Eeeve, 

 1842. 



