116 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. [VoLY. 



at the same rate, and the sides of the internal whorls become more ex- 

 posed, until in some old specimens they are only about half covered up. 



"Thick folds or ribs are present in some old specimens, and a tend- 

 ency to form nodes. In some large specimens, the ribs cross the abdo- 

 men, and in one fragment a curious effect is produced by the retention 

 of the constrictions formed by the transient mouths of the shell. These 

 make depressions with swellings between, which give the abdomen a 

 scalloped appearance, amply suflacient to found a new genus upon if 

 economically used. There may be two rows of slight nodes on either 

 side of the abdomen, giving this shell a slight resemblance to Trachy- 

 ceras in some cases. 



"The forward part of the living-chamber seems to be more rounded 

 or gibbous than the after part, which has the square abdomen, even in 

 old specimens; though I think that in extreme old age the whole shell 

 would exhibit a round abdomen and more gibbous sides. These peculi- 

 arities, and its flattened abdomen, might readily mislead an observer to 

 identify this species with Amm. semiimrtitus von Buch, but a glance at 

 the septa would satisfy any one that they are distinct."— (A. H.) 



Meekoceeas gracilitatis var.— Among the examples of Ji". gracili- 

 tatis which were obtained at locality ^o. 1 is one which shows a consid- 

 erable modification in the character of the septa. These appear to be in 

 all respects like those of the tjirlcal forms except as regards the inner 

 lateral cell and the auxiliary lobes and cells. The inner lateral cell is 

 smaller than in the typical forms, and its inner border is not so abruptly 

 defined from the auxihary series. This series occupies a wider space, 

 and consists of more numerous serrations than in the typical forms; 

 appearing, indeed, to consist of a finely serrated, nearly straight suture. 

 The umbilical shoulder is also less abrupt than in the typical forms. 

 Professor Hyatt thinks it may possibly prove to be a distinct species 

 when better known. 



Genus Aecestes Suess. 



Aecestes? cieratus White.— In his notes upon this coUection of 

 Cephalopods, Professor Hyatt refers this form provisionally to the genus 

 Arcestes with the following remarks : 



" The specimens are too fragmentary to tell with any certainty the 

 species ; and even the genus ought perhaps to be considered doubtful, 

 because the whole outline of the suture was not seen. The ^runzel- 

 schicht,' however, was so marked that this appeared to show them to 

 be identical with Arcestes. The septal sutures are, however, not entirely 

 unlike those of Gymnotoceras.^' 



There are only two specimens of this species in the collection, both of 

 which, it is true, are too imperfect to afford the means for the satis- 

 factory characterization of the species. The characters which are shown, 

 however, are quite sufficient for its identification; and for the conve- 



I 



