334 " PALEONTOLOGY OF NEW YORK. 



Observations. This term has been proposed for the species above men- 

 tioned, in which the development of the shell is of such an extravagant char- 

 acter as to have necessarily modified the functions and anatomy of the animal. 

 Though the internal markings of this species have not been described, it is 

 probable that they will prove not to vary materially from those of Productus, 

 and even the external features are but a result attained along a line of develop- 

 ment represented in such forms as P. striatus, Fischer, P. ermineus, de Koninck, 

 P. genuinus, Kutorga, and not resting with P. proboscideus, but attaining an ex- 

 treme in DE Koninck's species, P. Nystianus, in which the pedicle-valve is de- 

 veloped into two tubes, one on the frontal and one on the cardinal margin.* 

 De Koninck has shown that in this last-named species the formation of these 

 tubes is an accompaniment of decrepitude, and that the early stages of the shell 

 conform to the normal form of Productus. No thoroughly satisfactory explana- 

 tion of the function of these enrollments of the shell has been ofTei-ed. 

 De Koninck was disposed to regard them as passages for muscular fibers by 

 which the animal was attached and d'Orbigny considered them as malformations. 

 The former view requires too radical a modification of the internal anatomy, 

 and, as to the latter, there can be no doubt that these tubes which are constant, 

 though variable in form, size and even in number, are altogether normal. The 

 further suggestion of d'Orbigny that the animal, from its constrained position, 

 possibly buried in the sediments, was forced to prolong its shell so as to reach 

 the surface of the sea-bottom, seems reasonable, and met with the endorsement 

 of Mr. Davidson. 



The group is probably represented in American faunas by the imperfectly 

 known P. clavus, Norwood and Pratten, from the Carboniferous of Illinois, a 

 form which seems to be a close ally of the P. proboscideus of Vist- and York- 

 shire. 



* See DB Koninok's tigiires of all these species ; Monogr. genre Productus, pis. i, vi, 



XIV. 



