PLEUROBONTE. 97 



The principal peculiarity of the shell of Thelidomus is the plate- 

 like baso-columellar lip, somewhat like that of Acavus or Macularia. 

 The anatomy exhibits considerable variation in some details, such 

 as the presence (pi. 23, fig. 24, lima) or absence (pi. 23, figs. 20-21, 

 auricoma v. havanensis*) of an appendix. The spermatheca duct is 

 much shorter than in Parthend. Many more species must be invest- 

 igated before a satisfactory account can be given of the peculiarities 

 of the genitalia of Thelidomus and related groups. See Poey, 

 Memorias ; W. G. Biimey, Proc. Acad. Nat. Sci. Phila. 1875, and 

 Ann. N. Y. Acad. ; Semper, Reisen, pi. 15. The eggs are oval, 

 white and calcareous-shelled ; the embryonic shell is densely gran- 

 ula^kd in the typical forms, shining and radially grooved in the 

 Cuban group which I have called Zachrysia. The latter are said to 

 form a calcareous epiphragm. 



(Thelidomus s. sir., species of Jamaica, Porto Rico and Lesser 



Antilles}. 

 P. incerta Fer., v, 57. punctifera Lm. 



notabilis Fer. asperula Beck. 



curvidens Pfr. v. castrensis Pfr., v, 59. 



striolata Guild. P. aspera Fer., v, 59. 



alutaceaZgl. granosa Wood. 



vehitinoides Anton. P. cognata Fer., v, 59. 



ravnii Beck. P. discolor Fer., v, 60. 



P. lima Fer., v, 58. P. ? sanctselucise Smith, v, 198. 



(Zachrysia ; species of Cuba and Bahamas). 



P. petitiana Orb., v, 60. P. emarginata Gundl., v, 64. 



P. guanensis Poey, v, 61. P. bayamensis Pfr., v, 64. 



P. scabrosa Poey, v, 61. P. guantanamensis Poey, v, 65. 

 P. auricoma Fer., v, 62. v. proboscidea Pfr., v, 66. 



microstoma Lm. P. rangelina Pfr., v, 66. 



v. noscibilis Fer., v, 63. P. trinitaria Gundl., v, 67. 



v. havanensis Pils. P. baracoensis (Gut.) Poey, v,. 

 " zeta Pfr." v, 63. lamellicosta Pfr. [67. 



v. provisoria Pfr., v, 63. 



Section Polydontes Montfort. 

 Polydontes MONTF., Conch. Syst. ii, p. 154, type P. imperator. 



Shell large, depressed, imperforate or narrowly umbilicated, solid 

 and heavy ; the surface microscopically decussated. Whorls 4^-5,, 



