HELIX-ISOMERIA. 135 



1878, p. 72, t. 5, f. 5, 6, 7. H. adela ANGAS, loc. cit, p. 72, t. 5, f. 

 8, 9, 10. 



This is an excessively variable species, allied to H. guillarmodi, 

 but conspicuously umbilicated while that form is imperforate. 

 Figures 38,39, 40, of plate 17 of the Manual vol. iv, are copies of 

 Pfeiffer's original figures of costaricensis. Figures 20-22, and 23-25 

 of plate 18 (this volume) represent Mr. Angas' adela and boucardi 

 respectively, being copies of his figures. On plate 60 I have figured 

 four specimens selected from the Academy suite collected by GABB 

 and SWIFT. The variation in size and degree of depression of the 

 spire is sufficiently shown by the figures and measurements I have 

 given. 



The base is unicolored w r hite in all the specimens I have seen, and 

 the inside of the umbilicus is brown ; the spire may be either slightly 

 conical or depressed, and has from one to three bands, either broad 

 or narrow ; the umbilical tract is tinged with bright yellow. 



"Animal dark gray above, foot white. High hills only." (Gabb.*) 

 Lives on leaves of trees. 



Section IX. ISOMERIA Albers, 1850. 



Isomeria ALBERS, Die Heliceen, p. 160 (1850). ALBERS-MAR- 

 TEXS, Die Heliceen, ed. 2, p. 155 (1860). H. & A. ADAMS, Genera 

 Rec. Moll, ii, p. 200 (subg. Lucerna) PFEIFFER-CLESSIN, Noment. 

 Hel. Viv., 176 (1878). 



A group of large, dark, chestnut or chocolate colored shells, con- 

 fined to the Andes of Peru, Ecuador and Colombia, allied to 

 Labyrinthus, but with the mouth-parts less developed, the teeth 

 when present generally small. I have seen scarcely half of the 

 species, and although the characters are quite well marked, I have 

 not ventured to construct a " key " to the species. The color of the 

 lip is often variable, species in which it is normally white sometimes 

 having a brown tint on the edge ; when it is brown, there is a white 

 spot on its face at the point where the peripheral carina terminates ; 

 the back of the peristome is yellowish. Many of the species are 

 oblong, or transversely dilated in outline, seen from above, and this 

 modification is accompanied by a narrowing of the latter third of the 

 last whorl, and an inflation of its base; the peripheral carina is less 

 conspicuous or wholly lost on this portion, in most forms which are 

 so dilated. The parietal wall is generally covered by a thin, trans- 

 parent callous, which on its edge is thickened, opaque white, forming 



