CUBAN ANNULARiroAE TORRE AND BARTSCH 135 



KEY TO THE SPECIES OF THE SUBGENUS OPISTHOCOELEX 



Axial ribs closely spaced paradoxum 



Axial ribs distantly spaced simulans 



OPISTHOCOELICUM (OPISTHOCOELEX) PARADOXUM (Torre and Henderson) 



Shell elongate-ovate, pale yellow, unicolor or marked by narrow, 

 feebly interrupted spiral bands of brown, the elements of which are 

 arranged in both axial and spiral series. Nuclear whorls 2, inflated, 

 strongly rounded, microscopically granulose. The postnuclear whorls 

 are well rounded, the early ones marked by lamellar, scalloped, dis- 

 tantly spaced axial ribs. These ribs become more approximated on 

 the middle turns and quite closely spaced on the last whorl, where they 

 are separated by spaces not so wide as the ribs. The scallops on the 

 whorls are more strongly developed at the summit than at the periph- 

 ery, and on the early whorls the scallops at the periphery interlock 

 with those at the summit of the succeeding turn. The scallops are 

 absent on the last turn. Suture well impressed. Periphery strongly 

 rounded. Base rather long, strongly rounded, and marked by the 

 continuations of the axial ribs, which extend into the umbilical area, 

 and by several spiral cords on the parietal wall near the umbilical 

 edge. The last whorl is decidedly solute and the part between the 

 parietal peristome and the preceding turn is covered by a strong callus, 

 which extends also over the umbilicus, wliich it covers. This callus is 

 pinched in at the edge and is marked by slender, concentric laminae. 

 Aperture subcircular. Peristome simple, thin. The operculum is 

 heavy and large, and it extends beyond the edge of the peristome; 

 it cannot be withdrawn into the aperture. The operculum has an 

 almost subcentral nucleus, and is marked by retractively curved 

 radiating ridges, which extend to the periphery of the whorl, and wliich 

 become fused with the equivalent sculpture of the succeeding turns. 

 These radiating ridges are also fused laterally to form a solid plate, as 

 in Colobostylus. The siphon at the posterior angle of the aperture 

 passes into a varicial thickening behind the aperture, which connects 

 by a channel with the umbilicus, and breathing is established through 

 the hollow axis and the decollated tip of the shell. 



This species appears to range along the southern plain of the Cubitas 

 Mountains. 



We are recognizing three subspecies as follows : 



KEY TO THE SUBSPECIES OF OPISTHOCOELICUM (OPISTHOCOELEX) PARADOXUM 



Shell small, length of decollated shell less than 11 mm paradoxum 



Shell larger, length of decollated shell more than 13 mm. 



Whorls strongly rounded gibbosum 



Whorla slightly rounded magnum 



