176 UMBRACULtfM. 



Subgenus Umbraculum. Shell sinistral, with growth-lines and 

 some faint, low, wide-spaced radial ridges (page 117). 



Subgenus Hyalopatina Dall. Shell dextral, the nucleus siuistral ; 

 sculptured with very numerous radiating lines of minute elevated 

 points (page 184). 



See also, Bertinia Jousseaume (page 189). 



Genus TYLODIXA Kafinesque, 1819. 



Foot long-oval, without anterior sinus. Head large, with prom- 

 inent anterior tentacles. Gill a short bipinnate plume on the right 

 side posteriorly. Penis retractile, on the right side in front of the 

 gill. Shell with the edges not calcified, vertex subcentral (page 185). 



Genus UMBRACULUM Schumacher, 1817. 



Patella sp. of GMELIN, MARTYN and some other early authors. 



Acardo LAM., (in part), Syst. An. s. Vert., p. 130 (1801). 

 MEGERLE von MUHLFELD, Gesellsch. Naturforsch. Fr. Berl., Mag. 

 fur die Neuesten Entdeckungen, etc., v, p. 63 (1811). Not Acardo 

 Commercon MS. in Bruguiere, Encycl. Meth., i, p. 1 (1792),=Epi- 

 physis of whale, teste Deshayes, Encycl. Meth., edit. 1830, p. 1. 



Umbraculum SCHTMACHER, Essai Nouv. Syst. Yers Test., pp. 

 55, 177 (1817). 



Gastroplax BLALST., Bull. Sci. Soc. Philomathique for 1819, p. 

 182. 



Umbrella LAMARCK, Anim. s. Vert., vi, p. 343 (1819). 



Ombrella BLAINVILLE, Diet. Sci. Nat, xxxii, p. 267 (1824). 



Umbella ORB., Moll. Cuba, i, 115 (1841). 



Operculatum H. & A. AD., Gen. Rec. Moll., ii, p. 41 (1854;, and 

 of Linne, Mus. Tess., 1753, not binomial. 



Shell patelliform, depressed, sinistral ; the vertex to the left of and 

 somewhat behind the center, usually colored, more or less conically 

 elevated, apex curved backward, when perfect forming a minute 

 spiral of scarcely over one whorl. 



Soft parts much larger than the shell. Foot very voluminous, 

 tuberculate above, with the sole very broad, oval; deeply slit in 

 front, the mouth situated at the bottom of the sinus, with plate-like 

 labial processes in front of it. Head projecting but little in front of 

 mantle, bearing two tentacles slit down their outer sides, the small 

 eyes at their inner, anterior bases ; penis in front of head, lying in 



