Baker — A Revision of the Limnaeas of Northern Illinois. 7 



iDg ; spire sharply conical ; sutures very deeply indented ; 

 aperture elongately-ovate, somewhat expanded; peristome 

 thin, acute; columella thickened by a testaceous deposit, and 

 bearing a heavy plait across the middle; the columella is re- 

 flected at the lower end, the reflection almost covering the 

 umbilicus, which is narrowly open ; the umbilical region is 

 somewhat indented. The surface is sometimes broken up by 

 coarse, spiral semi-ridges, with facets forming a somewhat 

 reticulated surface. 



Length 12.00 

 " 12.00 

 " 10.00 

 " 8.75 

 u 13.00 



width 6.00; aperture length 6.00; width 3.00 mill. (8457.) 



« 5.25; " " 6.00; " 3.50 " (8457.) 



" 4.00; « " 5.50; " 2.50 " (8457.) 



" 5.00; " " 4.50; " 2.50 " (8457.) 



«« 5.75; " " 7.50; « 4.00 « (8468.) 



Fig. 3. Animal of 

 Limnaea desidio- 

 sa Say. ( Binney, 

 /. 25.) 



Animal (f. «?, after Binney) : With a very small, more or 

 less oblong foot, when viewed from the base, the anterior and 

 posterior borders rounded; color dark gray 

 or blackish, lighter below; the whole surface 

 is dotted with whitish, which is specially 

 noticeable about the ej'es ; tentacles trian- 

 gular, flat, short, more or less transparent; 

 the black eyes are placed on prominences at 

 the inner base of the tentacles ; respiratory 

 orifice on the right side, near the angle of 

 the peristome and body whorl. Length of 

 foot 5.00, width 3.00 mill. The heart is 

 situated near the umbilicus and the pulsations are very rapid ; 

 the writer counted 150 to 155 per minute. 



Jaw: As usual. 



Radula formula: ^ + f + 1 + i + | + | + ^ (46 — 1 

 — 46): central tooth as usual; lateral teeth with a subquad- 

 rate base of attachment, the reflection very broad, bicuspid, 

 the inner cusp long, reaching below the lower margin of the 

 base of attachment, the side cusps smaller; the 8 to 16 laterals 

 are tricuspid, the inner cusp very small; these may be called 

 intermediate marginals; marginals at first (17 to 20) modified 

 laterals, with a long, bifid inner cusp and two very short outer 

 cusps ; rest of marginals long and narrow, serrated, gen- 

 erally three short cusps at the distal end and two short>cusps 



