CHAPTER X 



TIM: L<>\VI<:R SILURIAN GASTROPODA 



OF MINNESOTA. 



i <, I. o. ri.Rli'H ANI> \V II 



INTRODUCTION. 



The Gastropoda are Mnlltixca with a more or leas 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 :m<l 



;ral 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 

 ii-k, developed upon the ventral side of the body, and not divided into distinct parts. 

 In certain types, however, the Hdtropoda especially, the foot exhibits a division into 

 three portions, an anterior, a middle and a posterior lobe, and besides forms either 

 a ventral tin. <>r a tin-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 a- tin- 



Beforr my part of the work on UM Lower Silurian Uulrvpuda of Minnesota could be InUbxd. my friend n<l colaborrr. 

 Mr. W. II. gooweld, died. ID bio death eelMoe ha. I<-t an earned and able. tl>oub loo modest, worker, the Geological and 

 .Natural History Survey of Mlooeaoia one of lu beat friend*, and the wurl.l a true man. In Inlahlog Ike work with. 

 aeahrtuce. I may here awl there hare taken a Maud that he mlf ht DO* hare auctioned. Boon- of the material > 

 deecrlbed a* lew. he ne*er aw. and. a* It would be unju.t to tuakr him bear half Hie mpniMlblllty In theee ca. I have 

 thought It right to dUtlnguUn neh tpeelea by placing my own aante la parentheata after the propoMd oan.p. 

 wUh It ui be nndentood Uiat whatever credit may attach to the foil.,, n..- w..rk Mr. Sooncld baa erery right Ui chare It M I. 

 me. On the other hand, permit nte aloeie to bear the blame tor the error. iu:;. n 



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