COELOCENTRUM. 31 



visible as a round, exactly central hole. The last whorl be- 

 comes shortly free in front, and is usually girt below the mid- 

 dle by a low cord. Aperture irregularly ovate or rounded, 

 the peristome continuous, narrowly reflexed throughout. 

 Internal axis a somewhat fusiform polished tube, smooth or 

 longitudinally costate. The usually deciduous early whorls 

 taper gradually to the nepionic shell, which is rather large, 

 cylindric or club-like, composed of 4i/o-7 whorls, the first 

 smooth and bulbous, the rest more or less costulate. 



Type, C. turris Pfr. Distribution, southern and south- 

 eastern Mexico to Guatemala, with an aberrant group in 

 Lower California. 



The soft anatomy is known by Strebel's dissection of a 

 specimen of C. arctispira from near Misantla. 



Foot very long. The body lobes of the mantle consist of a 

 divided right, a left, and a posterior lobe. The salivary 

 glands are extremely loose masses around the first part of the 

 oesophagus and retractor. The transverse rows of the radula 

 imbricate so that the ends of the cusps reach to the beginning 

 of those in the next row. The central teeth have small side- 

 cusps, laterals with an ectocone (pi. 19, fig. 44). The foun- 

 dation of the jaw (pi. 19, fig. 41) is a structureless, hyaline 

 membrane, bordering the true horn-colored smooth jaw on all 

 sides, projecting rather broadly between the ends and the 

 large median projection. The penis is very short and wide, 

 with terminal retractor, the v. d. inserted beyond the middle. 

 Spermathecal duct long (pi. 19, fig. 42). The retractor mus- 

 cle (pi. 19, fig. 43) of the left tentacle is united to that of the 

 pharynx proximally, that of the right tentacle being free, but 

 there are slender bands running from the pharyngeal re- 

 tractor to both tentacular retractors anteriorly. There is no 

 muscular plate over the pharynx, as in Eucaludiuin. Two 

 long muscles arise from the columellar muscle and pass for- 

 ward to the mantle-edge. 



I. Species of moderately large calibre, normally losing 

 many of the early whorls by autotomy. 



1. Internal axis large, with a sub-median (spiral) 

 swelling within each whorl, crossed by numerous 



