BEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 489 



river and Trenton periods, our forms appear to be somewhat primi- 

 tive, partly in the j-elatively smaller and less nummuloidal siphuncle 

 and partly in the restriction of the organic deposits to the earlier 

 growth stages, at least in one of the two species. 



A reference to the subgenus Paractinoceras Hyatt, that is described 

 as exhibiting a similar restriction of the rosettes in its middle stages 

 as suggested in our material, is excluded by the long and slender 

 form of the species of that genus. 



Another genus, Cyrtactinoceras, has been erected by Hyatt in the 

 chapter on cephalopods in Zittel-Eastman but not described and 

 based on the citation of Cyrtoceras rebelle Barrande as 

 genotype. That form proves to be a cyrtoceraconic species with de- 

 pressed section, rather closely arranged septa, moderately nummu- 

 loidal siphuncle which shrinks somewhat in old age, is filled in the 

 middle stages with rosettes, located near the convex side of the conch 

 but somewhat variable in position and approaching the center again 

 in old age. To this species the forms here brought under the Actin- 

 oceratidae approach in the somewhat stout form of the conchs, 

 their depressed sections, and the characters of the siphuncles, nearer 

 than to any other group, and we have, therefore, united them under 

 the same generic term. 



Cyrtactinoceras boycii Whitfield (sp.) 



Plate 35, figure 1-4 



Cyrtoceras boycii Whitfield. Am. Mus. Nat. Hist. Bui 1886 

 I '.320, pi. 29, fig. 4 ■ " 



From the original description and our own material the follow- 

 mg diagnosis can be given for this interesting form : 



A rather stout, strongly convex cyrtoceracone with depressed 

 elliptic section, the major and minor diameters of which have an 

 approximate ratio of 6:7; expanding rather rapidly (at the rate of 

 1 mm in 3 mm), while its curvature decreases slightly with advanc- 



ling age; the hight of an arc of 30 mm in the apical portion being 



■ 5 mm and in the mature portion but 2 mm. 



The cameras are shallow, specially so in the apical portion, where 



.20 may be counted within the space of 20 mm, but increase some- 

 what fast in depth in apertural direction and in the most advanced 



^ stage observed only 9 were found in the same space. The living 

 chamber has been observed only in one specimen, where it is ex''- 

 panding rapidly and has a length of 36 mm, though probably not 

 quite complete, and a basal width of 25 mm. The aperture has not 

 been seen. 



