216 BULLETIN 192, UNITED STATES NATIONAL MUSEUM 



Axial ribs are always present, varying in different groups from slender, 

 hairlike elements to lamellae; their spacing varies widely in different 

 groups. Fine microscopic axial threads may or may not be present be- 

 tween the heavier ribs. The spiral sculpture may consist of strong 

 cords that may be present on all parts of the surface, or it may be re- 

 stricted to the umbilicus, or may be entirely absent. The last whorl may 

 be solute or adnate to the preceding turn. The umbilicus presents a wide 

 range of variances. It may be narrow or wide, open or closed. The aper- 

 ture also presents considerable difference, varying from oval to sub- 

 circular, with the peristome always double; the inner peristome may be 

 slightly or somewhat exserted; the outer peristome ranges from nar- 

 row to broadly expanded in different species and this expansion may 

 extend over the entire Hp or it may characterize only part of it. An 

 auricle may or may not be present at the posterior angle. The operculum 

 has the whorls separated by a narrow, deep groove, which on the last 

 whorl constitutes the plain chondroid edge. The parts of the whorls 

 between this inner edge and the groove are crossed by numerous, re- 

 tractively curved, decidedly strongly raised lamellae separated by nar- 

 row spaces. Behind the aperture is the breathing siphon, upon which 

 the generic name is based. This tube communicates by a puncture with 

 the interior of the aperture near the posterior angle, slightly behind the 

 edge of the peristome. The siphonal tube is usually directed upward and 

 backward into the suture, though in a number of species with closed 

 umbilicus the tube does not communicate at once with the free surface, 

 but with a channel situated behind the broadly expanded, adnate parietal 

 peristome of the outer lip, which in turn communicates with the hollow 

 axis of the shell, and through this with the exterior through the de- 

 collated apex of the shell. 



Type species : Ctenopoma bahamense Shuttleworth = Opistho siphon 

 (Opisthosiphon) bahamensis (Shuttleworth). 



By an error, the name Opisthosolen crept into Ball's "List of Bahama 

 Land Shells" where on page 42^ are listed : 

 Opisthosolen hiforme Pfr. 

 Opisthosolen hiforme var. bahamensis Shuttl. 

 Opisthosolen rawsoni Pfr. 



An errata slip at the end of the volume states: "Owing to the fact 

 that the author did not see final proofs of this paper some corrections 

 are needed : 



"Page 42, line 30 from top, for 'Opisthosolen' read Chondropoma. 



"Line 32 from top, for 'Opisthosolen biformis var.' read Opisthosiphon 

 bahamensis. 



"Line 33 from top, for 'Opisthosolen' read Opisthosiphon. 



"Line 36 is to be deleted entirely." 



In order that there may never be a question about the nonavailability 



1 The Bahama Islands. Geogr. Soc. Baltimore, May 1905. 



