344 



GEOLOGICAL SURVEY OF TEXAS. 



Isle of Man, from Carboniferous, is another form of this genus having a 

 very slight form of involution, with a compressed whorl and sub-acute ab- 

 domen. The involution is very slight in this species, exposing all the inter- 

 nal whorls, but in the transverse section of the outer whorl and in the sutures 

 it is unquestionably related to the species described above. The living cham- 

 ber is over one half of a volution in length, but it is not certain from the 

 drawing that it is completed. 



The species differs from (Discites) 

 Highlandense, Meek and Worthen,* 

 in being much larger, in having 

 stouter whorls. The sutures are, 

 however, evidently very similar. 

 Highlandense is described as having 

 a narrow periphery, whereas this 

 shell when about the same size as 

 the specimen figured in the Illinois 

 survey has an abdomen almost as 

 broad as the dorsum and very much 

 broader proportionately than in its 

 own adult whorl. It differs from 

 (Naut.) planovolve, Shumard,f in size 

 and in having whorls with more 

 rapid growth, and probably a wider 

 and deeper umbilicus than in that 

 species. Fig. 47. 



It differs from the nearest European congener, Kon. infundibulum, as figured 

 by De Koninck,J in having a narrower abdomen and a more compressed form 

 of whorl in the adolescent and adult stages; also in the sutures, which have 

 a more marked abdominal lobe. It differs from Kon. (Nautilus) podolskense, 

 Marie Tzwetaev,|| in the young. This is similar to' the adult in the propor- 

 tions of the parts, but in K podolskense the young whorl has an abdomen 

 broader than the dorsum. The adult of this species also has a broader abdo- 

 men than the adult of our shell. The species evidently stands just between 

 the genus represented by such species as Kon. ingens, implicatum, described 

 by De Koninck, and K. podolskense, all of which have stout whorls with broad 

 abdomens, and whorls similar to those of the young of K. umbilicatum, and 



* Geol. IUinois, VI, p. 531, PL 33, Pig. 2. 



f Trans. St. Louis Acad., I, p. 190. 



% Calc. Carb., PL 24. 



|| Ceph. du Calc. Carb. de la Russie Centrale, PL 3. 



