142 PKOCEEDINGS OF THE NATIONAL MUSEUM Vol.89 



the ribs and they are marked by microscopic axial threads; no spiral 

 threads are present on the spire. Suture strongly constricted. 

 Periphery somewhat inflated, well rounded. Base moderately long, 

 well roimded, marked by the continuation of the axial ribs, which 

 extend to the plugged umbilicus. Outside of the umbilical closure 

 there are 3 or 4 spiral cords, which render the axial ribs decidedly 

 scalloped at their junction. Aperture very broadly oval, almost 

 subcircular; peristome double, the inner somewhat exserted, not 

 reflected; the outer broadly expanded and marked by concentric 

 lamellae, deeply notched on the inner lip, posterior to which it is 

 reflected into the umbilicus, which it plugs. Operculum and siphon 

 typically opisthocoelid. 



We are recognizing two subspecies, which the foHowing key and 

 descriptions will differentiate: 



KEY TO THE SUBSPECIES OF OPISTHOCOELICUM (OPISTHOCOELICUM) LAMELLICOS- 



TATUM 



Axial ribs decidedly lamellar and decidedly scalloped mabuyense 



Axial ribs not decidedly lamellar or decidedly scalloped laraellicostatuin 



OPISTHOCOELICUM (OPISTHOCOELICUM) LAMELLICOSTATUM MABUYENSE, new 



subspecies 



Plate 9, Figure 6 



This race comes from Mabuya, near Florencia, Camagiiey Province. 

 It differs from typical 0. (0.) lamellicostatum lamellicostatum in being 

 of much darker color and in having the axial ribs decidedly lamellar 

 and decidedly scaUoped. 



The type, U.S.N.M. No. 535481, has 24 axial ribs on the first of the 

 remaining turns and 34 on the last; it has 4.2 whorls remaining and 

 measures: Length, 11.2 mm.; greater diameter, 6.6 mm.; lesser 

 diameter, 5.0 mm. 



OPISTHOCOELICUM (OPISTHOCOELICUM) LAMELLICOSTATUM LAMELLICOSTATUM 



(Torre and Henderson) 



Plate 9, Figure 5 



1921. Opisthosiphon (Opisthosiphon) lamellicostatum Torre and Henderson. 

 Proc. U. S. Nat. Mus., vol. 59, pp. 263-264, pi. 42, figs. 6. 7. 



This, the typical race, was collected by Torre at Boqueron del 

 Jatibonico on the boundary of Santa Clara Province. It is easily 

 distinguished from the other subspecies by its less strongly developed 

 axial ribs, which are also much less scaUoped. 



The type, U.S.N.M. No. 314963, has 25 axial ribs on the first of the 

 remaining turns and 65 on the last; it has 4.2 whorls remaining and 

 measures: Length, 12.0 mm.; greater diameter, 7.0 mm.; lesser 

 diameter, 5.5 mm. 



