NATURAL SCIENCES OF PHILADELPHIA. 51 



plate. Marginals quadrate, of equal width and height, with two 

 short, wide, Munt, round cusps, the inner one slightly the larger. 



Helix discolor, Fer. (Thelidomns). 



Jaw arcuate, thick, ends blunt. Anterior surface with 7 un- 

 equal, decided, stout ribs, denticulating either margin. 



Lingual membrane (plate X.,lig. 1) long and narrow. Centrals 

 with a long narrow plate expanded at the base, and bearing at its 

 corners a small reinforcement ; base of the plate extending be- 

 yond the cusp ; bluntl}^ tricuspid, the median cusp long, stout, 

 with a short blunt point ; side Cusps subobsolete. Laterals as in 

 the centrals, but unsym metrical, and with a shorter plate. Mar- 

 ginals quadrate, wide as higli, with two short, blunt denticles, 

 the inner one slightly the longer. 



Helix lima, Fer. {Thelidomns) . 



Porto I\ico. Received mounted from tbe late Mr. Robert 

 Swift. 



Jaw arcuate, thick, high, ends blunt ; no median projection to 

 the cutting edge. Anterior surface with 7 stout ribs. A strong, 

 thick muscular attachment to the upper margin. 



No lingual membrane received. 



Helix marginella, Gmel. (Caracohts). 



Porto Rico. Received mounted from the late Mr. Robert Swift. 



A portion only of the jaw is preserved on the slide. It appears 

 to be thick, arcuate, with strong transverse lines of reinforce- 

 ment and decided ribs. 



Lingual dentition as in H. excellens (see plate X., fig. 67). 



Helix Chemnitziana, Pfr. (Pleiirodonta). 



Jamaica. Received mounted from the late Mr. Robert Swift. 



Jaw stout, arched, ends attenuated, blunt ; anterior surface 

 with about 6 irregularly disposed ribs, stout and denticulating 

 either margin. 



No lingual membrane received. 



Helix Carmelita, Fer. (Pleurodonta). 



Jamaica. Received mounted from the late Mr. Robert Swift. 



Jaw arcuate, ends blunt, anterior surface with about 6 stout 

 ribs, denticulating either margin. 



Lingual membrane (plate X., fig. 5) as usual in the Helicidse. 

 Central teeth short, bluntly pointed on the middle cusps, the 

 side cusps subobsolete ; laterals like centrals, also with obsolete 



