62 NEW-YORK FAUNA MOLLUSCA. 



Planorbis OBLIQUUS. 



PLATE IV. FIG. 57. A. B. 



(STATE COLLECTION.) 



Description. Shell depressed, discoidal. Volutions four ; the surface shining, with regulai 

 minute incremental lines ; the body-whorl obsoletely subangular below. Spire nearly as much 

 depressed as the umbilicus, which latter is large, and exhibits all the volutions to the apex : 

 suture distinct ; body-whorl not distinctly deflected from the plane of the other volutions. 

 Mouth unarmed, very oblique. 



Color, dull olive. 



Diameter, 0-3. Height, 0*1. 



The specimens of this species were obtained from the Mohawk, and from Newcomb's 

 pond in Pittstown, and presented by Dr. B. W. Budd of this city. Some eminent concholo- 

 gists suppose it to be a variety of the deflectus of Say ; but from this it differs by the obli- 

 quity of the mouth when turned downwards, and has no acute lateral edge as in that species. 

 The concavus of Anthony, of which I have seen specimens but no description, may possibly 

 be the young of this, but at all events is a closely allied species. 



Planorbis armigerus. 



PLATE IV. FIG. 64. a. b. c. 



(STATE COLLECTION.) 



Planorbis armigerus. Say, Jour. Acad. Nat. Scienees, Vol. 2, p. 164. 



P. id. Adams, American Journal of Science, Vol.40, p. 269. 



Discus id. Haldeman, Monograph of the Limniades, No. 1. 



Planorbis d. Gould, Invertebrata of Massachusetts, p. 205, fig. 138. 



Description. Shell small, obsoletely wrinkled. Upper surface slightly concave ; the suture 

 distinct. Whorls four, with minute revolving lines on the under side. Umbilicus deep, ex- 

 hibiting all the volutions. Aperture very oblique, with the carina continued to its edge. 

 Throat armed with five teeth, which are large, white, and nearly fill the aperture ; two on 

 the pillar-lip, one of which is large and oblique, with a smaller one near it ; on the lip a pro- 

 minent lamelliform tooth near the base, with two small oblique ones above. 



Color. Light olive brown. Animal dusky bluish. 



Diameter of the shell, 0'3. Height, 0*1. 



Common in swamps and ponds in all parts of the State. The teeth, which form so re- 

 markable a character in this species, are so far within the aperture as not to be obvious at 

 first sight ; they are exceedingly irregular, not only in their shape, but distribution ; their 

 general form and arrangement, however, corresponds very well with the description given by 

 Mr. Say. This and corpulentus are described as dextral shells. 



