90 ENDODONTIDAE 



Genus PUNCTUM Morse 



The genus Punctum is composed of minute snails with strong 

 vertical and longitudinal lines of growth. Several species live in 

 the United States but only one of these species occurs in Illinois. 

 This genus was founded by Professor E. S. Morse in 1868, his 

 type species being the Helix pygmaea of Draparnaud, which he 

 showed to be the same species as the Helix minutissima of Dr. 

 Isaac Lea, who was a noted specialist in the study of river 

 mussels or Unionidae. 



PUNCTUM PYGMAEUM (Draparnaud) 



Except Striatura milium, a species of the family Zonitidae, 

 Punctum pygmaeum is the smallest species of land snail inhabit- 

 ing Illinois. Its reddish, horn-colored shell, less than one-six- 

 teenth inch ( 1.5 mm.) in diameter, 

 is globose. This shell has 4 convex 

 whorls which are finely striated 

 with growth lines crossed by spiral 

 lines so fine that a microscope must 

 be used to see them. It has a wide 

 and deep umbilicus. The tiny shell 

 of Punctum pygmaeum may be dis- 

 tinguished from that of Striatura milium by its more globose 

 form, narrower umbilicus and particularly by the absence of the 

 conspicuous riblike folds which mark the surface of the shell 

 of milium. 



The small pygmaeum snail, which is apparently rare in 

 Illinois, has been recorded from only five counties: McHenry, 

 Cook, Will, Washington and Jackson. These localities cover a 

 large part of the state from north to south, indicating that the 

 species is widely distributed in Illinois. 



The very small size of Punctum pygmaeum has caused 

 students and collectors to overlook it. They may search for it 

 beneath the bark of fallen tree trunks, on small limbs and twigs 

 of fallen timber, in forest debris and in similar places. It is a 

 forest snail living with other forest-loving species, such as 

 Helicodiscus parallelus, Zonitoides arboreus and Discus patulus. 

 It lives in both North America and Europe, and is very widely 

 distributed in the two continents. 



