200 LAND AND FRESHWATER 
theory of Darwin, their modified descendants possess the organiza- 
tion, in a more or less perfect condition, which was essential to their 
predecessors, but is no longer equally necessary to their own exist- 
ence, and that, in short, the various apertural slits and imperforate 
tubes of Pterocyclos, Pupina, Alyceus, &e., must be regarded in the 
same light as rudimentary organs. By this hypothesis, also, we can 
understand the appearance of the more perfect conditions for com- 
munication between the atmosphere and the lung-chamber of the 
animal in widely separated forms, while others closely allied to each 
of them are more or less deficient in all traces of a similar organiza- 
tion, and the occurrence of a gradual passage from tube-bearing 
genera to others totally destitute of any modification of the peristome 
or suture is perfectly natural. The tube of Spiraculum becomes an 
incision in the peristome in Pterocyclos, the Burmese forms of which 
are closely alhed to species of Cyclophorus like C. calyx, Bens., 
which have a thickened operculum and » minute rudimentary wing- 
shaped projection of the outer lip, close to the suture; and from 
these forms, again, there is a passage to discoid species, like C. 
stenostomus, Sow., with perfect peristomes. In the same way we 
may pass from Raphaulus, through Pupinella and Pupina, to 
Registoma, and finally to Callia, and through Cataulus to Megalo- 
mastoma. To the subject of the affinities of these various genera, 
however, and especially of the aberrant Alyccus, I hope to refer in 
a future communication.” 
RHAPHAULUS PacuysIPHON, Theob. & Stol. (Plate XLVII. figs, 3, 
3d.) 
Rhaphaulus pachysiphon, Theobald & Stoliczka, Journ. A. S. B. 
1872, vol.xli.<p..329, pl. xi, feed. 
Rhaphaulus , Hanley, Conch. Ind. p. 53, pl. exxxiii. fig. 4. 
Rhaphaulus , Theob. Supp. Cat. p. 40; Nevill, Hand-list, 
p. 302. 
Original description :—‘ R. testa cylindraceo-ovata, anguste per- 
forata, solida, fusca ; spira obtusa, apice ad latus inclinato, excentrico ; 
anfractibus 54 convexiusculis, transversim confertissime striolatis, ad 
suturam simplicem adpressis; anfractu penultimo sensim, ultimo 
valde, descendente, primo supra aperturam deplanato, altero ad 
suturam paulo constricto, ad basin convexiusculo ; apertura fere verti- 
cali, circulart, peristomate pallide fuscescente, plane expanso atque 
crasso, supra ad anfractum penultimum labio attenuato et fere horizonti 
adnato, postice (aut supra) ad suturam tubulo crasso, deflewo instructo. 
Long. 12°6, lat. anf. penult. 7-6, diam. apert. cum perist. 6°2, apert. 
int. 3°6 mm. 
“« Hab. prope Moulmain, valle Ataran fluminis. 
“ A rare and very distinct form from any of the other known species 
by its distorted spire and externally bent down sutural tube.” 
RHAPHAULUs cHRysALIS, Pfeiffer. (Plate XLVII. figs. 1, 1 a.) 
Cyclostoma chrysalis, Pfeiffer, P. Z.S. 1852, p. 158. 
Anaulus chrysalis, Benson, A. M. N. H. 1856, vol. xiii. p, 342. 
