New Land Shells from Costa Rica. 259 



right of the mantle margin, slightly in advance of the centre: genital and 

 anal orifices — ? * 



Shell internal (pi. xi, fig. J) rudimentary, unguiform, large, membranous, 

 protected by an epidermis ?, without distinct septa, a spiral arrangement, 

 indicated above by depressed lines, below by raised ridges. 



Jaw (pi. xi, fig. I) high, solid, decidedly arched, ends scarcely attenuated ; 

 anterior surface with a few stout ribs, denticulating the lower margin. 



Lingual membrane (pi. xi, fig. K) as usual in Polygyra, Stenotrema, &c. 

 Long and narrow. Central teeth tricuspid, laterals bicuspid; marginals 

 quadrate, irregularly bicuspid, the inner cutting points the larger and 

 bifid. 



Known only by G. Gabbi, described below. 



This curious slug may at once be distinguished from all 

 others by its rudimentary shell, entirely concealed by the 

 mantle, and of about similar size. The shell has no distinct 

 whorls, but a spiral arrangement is indicated on the upper sur- 

 face by impressed lines, on the lower surface by a raised spiral 

 ridge. The edge of this ridge is reflected, in dried specimens, 

 for about one-half whorl, giving a Haliotis-like character to 

 the shell. The shells of Marietta, Gceotis, and Parmella are 

 somewhat similar to this, but those genera differ widely in 

 their other characters, especially the jaw and lingual dentition. 

 Indeed, there is no known slug combining all the generic 

 characters of this, so that I am forced to suggest a generic 

 name. 



The dried animal reminds me of Sempe/'s figure (Phil. 

 Arch.) of dried Vitrinopsis, on account of the small size of 

 the dried body compared to that of the shell. 



* Animal limaciforme, subcylindricum, postice attenuatum. Pallium sub- 

 centrale, tenue, paululum anterior, parvum, ovatum, testam includens. 

 Discus gressorius ? Porus mucosus nullus. Apertura respiratoria ad dex- 

 tram pallii in parte vix anteriori marginis Apertura genitalis et analis — ? 



Testa interna, magna, membranacea, (epidermide protecta ?) unguiformis 

 paucispira. 



Maxilla solida, valde arcuata, costis paucis validis exarata. 



Lamina lingualis ut in Polygyra, Stenotrema, &c. Dentes centrales tricus- 

 pidatse, laterales bicuspidatae, marginales quadratae, irregulariter bicuspid- 

 atse, papillis internis majoribus, bifidis. 



