(CIEL NEI ey Oe. 
TISUB ICO Wms SIOLU EIDAUN Goetedia(Ole QuD va 
OF MINNESOTA. 
BY E. O. ULRICH AND W. H. SCOFIELD.* 
INTRODUCTION. 
The Gastropoda are Mollusca with a more or less distinct head and a well 
developed tongue which as a rule is armed with a plate or band set with teeth. The 
body is nearly always more or less unsymmetrical, the mantle never divided 
into two lobes, and the shell, when one is present, is univalve, except in the chitons 
in which it consists of numerous pieces. The “foot” is generally well developed, 
broad and horizontally expanded, being used by the animal in creeping about; or it 
may be variously modified to adapt it for swimming or burrowing purposes. The 
eyes and organs of feeling and hearing are contained in the head, while the viscera 
(organs of alimentation, reproduction, etc.) are found in the posterior portion of 
the body. 
Three principal portions are distinguishable in the body,—head, foot and 
visceral sac,—the last of these being protected by a fold of the dorsal integument 
called the “mantle.” ‘Typically, the foot is in the form of a flattened muscular 
disk, developed upon the ventral side of the body, and not divided into distinct parts. 
In certain types, however, the Heteropoda especially, the foot exhibits a division into 
three portions,—an anterior, a middle and a posterior lobe,—and besides forms either 
a ventral fin, or a fin-like tail, by means of which the animal swims, the back down 
wards. 
The head is usually very distinct and is generally provided with tentacles and 
eyes. Within the pharynx is found the singular dental apparatus known as the 
* Before my part of the work on the Lower Silurian Gastropoda of Minnesota could be finished, my friend and colaborer, 
Mr. W. H. Scofield, died. In his death science has lost an earnest and able, though too modest, worker, the Geological and 
Natural History Survey of Minnesota one of its best friends, and the world a true man. In finishing the work without his 
assistance, I may here and there have taken a stand that he might not have sanctioned. Some of the material which is 
described as new, he never saw, and, as it would be unjust to make him bear half the responsibility in these cases, I have 
thought it right to distinguish such species by placing my own name in parenthesis after the proposed names. Further, I 
wish it to be understood that whatever credit may attach to the following work Mr. Scofield has every right to share it with 
me. On the other hand, permit me alone to bear the blame for the errors. E. O, ULRICH. 
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