142 ANNALS NEW YORE ACADEMY OF SCIENCES 



Cephalopoda 



Orthoceras tuba sp. nov. 



Orthoceratoid shells are abundant in the Wewoka formation and many of 

 them possess the singular feature of accelerated expansion, so that they flare 

 conspicuously at the larger end, and, if the tendency were carried out to a 

 high degree, the complete shell would have a trumpet-shape, a configuration 

 which many of them even now suggest. This peculiarity, however, is mani- 

 fested in shells of very various sizes and presumably corresponding ages, and 

 it is found in both the chamber of habitation and in the septate portion. 

 Both hypotheses — that the flaring condition is a feature of maturity (which 

 is the natural supposition) and that it is the normal shape at all stages, the 

 expanded portion being resorbed so that the shell is regularly conical except 

 toward the aperture — are repugnant to the fact that the flaring portion is 

 sometimes septate. On the former hypothesis, furthermore, we must also 

 infer that the mature condition is in some specimens enormously accelerated 

 or retarded. 



Correlated with the peculiarity above described is found a relatively rapid 

 rate of expansion, giving the regular portion of the cone a rather strong 

 taper. The siphuncle is conspicuously excentric, though this character has 

 been seen in only a few individuals which at the same time have the trumpet- 

 shape in a conspicuoiis degree. The septation is rather frequent, about 4.5 

 to 5 chambers occurring within the distance of a diameter. 



None of the shells having the characters enumerated possesses the 

 peculiar secondary deposits of Pseudorthoceras. Indeed, they have the 

 chambers filled with ochreous clay, and it is difficult to understand how 

 this condition came about when the partitions are still retained. Possi- 

 bly the fine mud permeated the chambers through the siphuncle, which 

 seems seldom to be preserved in the specimens examined. For the most 

 part, these are internal molds, but in some instances they retain a sub- 

 stantial outer investment. 



With typical 0. tuba I am provisionally including a group of specimens 

 which do not show the expanded aperture, but have a similarly excentric 

 siphuncle and similarly frequent partitions. They vary much in size and 

 some of them are much larger than some of those which show the acceler- 

 ated expansion, but in view of the extreme variation in size of the speci- 

 mens possessing the latter character, it seems that this fact alone can 

 hardly be regarded as forbidding their union under a single species. This, 

 of course, would only be done on the hypothesis, either that the trumpet 

 shape was not a character of importance, or that these specimens, all of 

 which are naturally now imperfect, possessed it or would have possessed 

 it in the complete and mature condition. 



