344
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 abdomen. The involution is very slight in this species, exposing all the internal 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 chamber 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, in size and in having whorls with more rapid growth, and probably a wider and deeper umbilicus than in that species.
It differs from the nearest European congener, Kon. infundibulum, as figured by De Koninck, 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 proportions 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 abdomen 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. Illinois, VI, p. 531, Pl. 33, Fig. 2.
Trans. St. Louis Acad., I, p. 190.
Calc. Carb., Pl. 24.
Ceph. du Calc. Carb. de la Russie Centrale, Pl. 3.