360 MEXICAN BOUND ABY SHELLS— BALL. vol.xix. 



tlie pillar and consequently without the resulting convex fascicle mar- 

 ginating the i)ervious axis; with a rounded and not excavated base; 

 with a ribbed and funicular nepionic apical stage instead of a smooth 

 and domelike one, with a jaw differing as elsewhere described from 

 the jaw of Khodca, and jtrobably by being oviparous. 



The dentition oi' Ehodea has not been figured, so no comparisons can 

 be made Avith it. PUcoJuunui is intimately related to the group of 

 Biilimiihis, including Lc^dobi/rsus and such species as B. artemesUi. It 

 is probably the result of special factors of the environment acting on 

 part of the same ])hylum. From them it differs by the persistence of a 

 gyrate colunu'lla in the last 2 whorls and the resulting pervious axis, 

 features which are absent from its nearest relative, B. artemesia. It is 

 probable that the South American Ehodea is a similar modification of 

 some local phylum, induced by analogous features in the environment. 



BULIMULUS (ORTHOTOMIUM) ARTEMESIA, W. G. Binney. 



(Plates XXXI, fig. G; XXXII, fig. 6.) 



BuUmulus {Lepiohiirsns) artemesia (W. G. Binney), Dall, Prot-. U. S. Nat. Miis., 

 XVI, p. 642. pi. I.XXII, fig. 5. 



In my paper above refered to, this species was placed in a subdivi- 

 sion of the section LeptohyrKus, characterized by the absence of the con- 

 cealed llange on the pillar which is so curious a feature of B. hriianti, 

 B. spirifcr^ and B. reseyiann.s. Dr. Cooi)er suj^posing his Colummi ramen- 

 tosa to belong to Rhodca, and observing the indications of affinity 

 between B. artemesia ixud his Coliniina ramentosa, criticises me for plac- 

 ing the former in the same group witli the Leptohyrsi { = Sonoriiia, Pils- 

 bry), and observes that it would better have been placed in Feroncvus 

 until it was certain that it does not belong with Columna { = Ehodea). 

 !N<)W BeroHa'us {ptipiformis) is a Chilian form, with the dome-shaped 

 smooth nucleus of Bostryx belonging to that region, and, while the gen- 

 eral outline is very like that of B. artemesia, the nuclear whorls are as 

 far as possible removed from the ribbed funicular form which character- 

 izes the species of Lower California. Consequently, though having but 

 a single specimen of the shell, the type of B. artemesia, I did not hesi- 

 tate to place it among the forms, which by propinquity, as well as 

 nepionic characters, were distinctly pointed out as related to it. On 

 the other hand, the shell has not a single one of the characters upon 

 which the true Ehodea must rely for its validity. Yet Dr. Cooper, judg- 

 ing the true T\hodea by the shells, which at fir.st under the name of 

 Columna he wrongly referred to it, was not incorrect in supposing these 

 to be related to B. artemesia. Tliey are very closely related to it, and, 

 without doubt, are derived from the same stock, and the similarity of 

 Columna (Cooper) to li']iode((, Adams, is dynamic and superficial and 

 not genetic, as I shall now proceed to show. 



In nearly all the Lower Californian BnlimnJi, from the great 7>. mon- 

 tezuma down to the small artemesia, the nepionic or nuclear whorls 



