56 



Report of the State Geologist. 



Septation. Septa, the evidences of discontinuous growth, are, in a certain 

 sense, to the interior of the shell what the ornamental varices are to the exterior. 



In the species under consideration the interval 

 between the septa, constituting the air cham- 

 bers or loculi, increases outward with some 

 degree of regularity, although relatively to 

 the diameter of the whorl there is a gradual 

 diminution in the depth of these chambers. 

 The statement is, of course, subject to excep- 

 tion especially in senile growth stages and 

 pathologic conditions. The more rapid multi- 

 plication of septa in post-ephebic stages has 

 been regarded as one of the normal accom- 

 paniments of senility, but it can not be 

 interpreted as a reiteration of infantile con- 

 ditions. Our observation shows that among 

 the Naples forms of Ma/ntic. intvt/mescens this 

 trait is seldom well expressed, sometimes only 

 in the less depth of the last air-chamber. In 

 some of the specimens from the Chemung fauna the crowding of the later septa 

 is a very striking feature. There is sufficient evidence that as far as this specific 

 type is concerned, gerontic multiplication of septa is best displayed in 

 its latest representatives. Attention is directed to a variation hereinafter 

 described as Mantic. accelerans / a shell of small size with the intumescens 

 suture fully developed but having all the visible air chambers extremely shal- 

 low and the septa nearly parallel. It is a form which has been observed in a 

 few instances in the Naples shales, and is to be interpreted as presenting in 

 its septation a prematurely gerontic condition. 



The diminution in the depth of the air chambers may manifest itself in any 

 part of any individual. It is well represented in the figure upon Plate II (1), 

 which shows a highly irregular crowding of the septa during a con- 

 siderable portion of the neanic stage of shell growth, and it is to be 

 distinguished from the senile repetition above described, which is the 

 outcome of normal processes, while this desultory manifestation may prove 

 to be pathologic. 



The adult mture. The character of the adult suture is expressed in the 

 adjoining figure. Its most striking element is the broad, ear-shaped lateral 

 saddle. On the exposed surface there are two additional saddles, a bluntly 



Figure 26. Manticoceras Pattersoni, vertical 

 section across an early ephebic whorl showing 

 how the septa may be transected in such a sec- 

 tion ; vl and vl\ ventral lobes of successive septa ; 

 sp\ cut edges of the nearer septum ; Is and It', 

 lateral saddles ; I and V, lateral lobes ; till, sub- 

 dorso-lateral lobe ; d, d', d", dorsal lobes of 

 three septa; S, sipho. 



