ANISOSPIRA. 25 



whorls rapidly contracting, followed above usually by a cylin- 

 dric whorl or two of far smaller calibre. The (deciduous) 

 young shell has a rather large apex, smooth at first, followed by 

 several straightly costulate whorls. Internal column straight 

 or weakly spiral, perforated, in the last whorl or two en- 

 circled by a median and a subbasal cord or lamella, not visible 

 in the circular or ovate aperture (pi. 11, figs. 1, 2, 4,7). 

 Soft anatomy unknown. Type A. li'ibmanni. (Gr. anisos un- 

 equal, and speira a coil, in allusion to the disparity between the 

 early and late whorls). 



Distribution, southern and southwestern Mexico. 

 This genus differs from Eucalodium in the rapid increase 

 in diameter which takes place at the inception of the adult 

 stage, and in the armature of the axial column, which is re- 

 stricted to the last two whorls. In Eucalodium the diameter 

 of the shell increases regularly, and the column is alike 

 throughout its length. Though the axis is minutely perfor- 

 ate, there is no such axial cavity as is found in Ccelocentrum. 

 The internal armature, as Strebel has noted, resembles that of 

 Holospira and Bostrickocentrum; and it also finds a parallel 

 in the Haitian group of large 'Urocoptis species. The last 

 whorl is only shortly free in front, and the peristome is but 

 very narrowly subreflexed or expanded. In most characters 

 of the shell A-nisospira resembles Jamaican species of Urocop- 

 tis of the group of U. sanguined; but it differs in the larger 

 nepionic shell and especially in the plug or septum of the 

 amputated spire, in which Anisospira resembles Eucalodium 

 and other Mexican genera, and not the Antillean forms. 



Key to species of Anisosirira. 



I. Shell thin, very finely and densely rib-striate ; a lamella 

 encircling the pillar within the penultimate or the last 

 whorl. 



1. Diam. about one-third the length; white, 



a. whorls iy 2 to 9 ; internal lamella at base of pillar, 



iy 2 whorls long, A. dalli. 



~b. whorls 10-13, A. hyalina, 



2. Diam. contained about 2% times in length ; yellow- 



