CUBAN ANNULiARIIDAE — TOKRE AND BARTSCH 149 



by lamellar axial riblets, which vary materially in strength ; usually a 

 group of several weak elements is succeeded by a strong one. The 

 stronger ribs become expanded at the summit into auricles. The 

 axial riblets are decidedly wavy, which would indicate spiral threads, 

 but these are not apparent in the intercostal spaces. Of these ribs 

 36 occur on the first whorl, 48 on the second, 83 on the third, and 96 

 on the last. Suture strongly constricted. Periphery strongly 

 rounded. Base moderately long, strongly rounded, marked by the 

 continuation of the axial ribs, and within the umbilicus by spiral 

 cords, which render the axial ribs decidedly scalloped at their junctions. 

 The base is narrowly, openly umbUicated. The last whorl is solute 

 for about one-tenth of a turn. Aperture subcircular; peristome 

 double, the inner very slightly exserted; the outer very broadly 

 expanded on the parietal and inner lip, less so on the outer lip and 

 narrowest on the basal lip, marked by concentric lamellae. Oper- 

 culum typically torrellid. The siphon is at the posterior angle of 

 the aperture, short, and flexed into the suture, where it is marked 

 by a series of rings. 



The type, U.S.N.M. No. 535536, comes from Magua, Trinidad, 

 Santa Clara Province. It has 4.1 whorls remaining and measures: 

 Length, 7.0 mm.; greater diameter, 3.6 mm.; lesser diameter, 3.3 mm. 



This species is readily distinguished from T. (T.) simpsoni by the 

 broadly expanded inner lip of the outer peristome. 



Genus RHYTIDOPOMA Sykes 



1901. Rhyiidopoma Sykes, Journ. Malac, vol. 8, p. 60. 



Shell elongate-conic, axial riblets and spiral threads present in all 

 the known species; the axial sculpture is usually stronger than the 

 spiral. A recurved breathing siphon is present a little behind the 

 peristome at the junction of the parietal and the outer wall. Oper- 

 culum with the ribs not completely covering the whorls, thus showing 

 the basal chondroid plate in a narrow sinus, which marks the outer 

 edge of the turns. Both the inner and outer ends of the retractively 

 curved ribs are fused into lamellae, which are considerably higher 

 than the ribs, which extend in a gentle, retractive curve between 

 the lamellae. 



Type: Rhyiidopoma rugulosum (Pfeiffer). 



KEY TO THE SPECIES OF THE GENUS RHYTIDOPOMA 



Umbilicus closed by the reflected peristome honestum 



Umbilicus not closed by the reflected peristome. 

 Last whorl adnate. 



Outer peristome fluted coronatum 



Outer peristome not fluted nodulatum 



