ORTHOCERAS SOLLASI. 23 



Oethocekas Sollasi, A. H. Foord. Plate VIII, figs. 1 a — f. 



OfiTiiocERAS Sollasi, A. H. Foord. Ueber die Orthoceren des Kohlenkalks 



(Carboniferous Limestone) von Jrland. . . . In- 

 augural-Dissertation zur Erlangung der Doktorwiirde 

 der Kgl. bayer. Ludwig-Maximilians-Universitat 

 zu Munchen, |>. 32. 



Description. — Shell straight, of medium size, tapering at the rate of 1 in 8. 

 Section slightly elliptical, the ratio of the two diameters as 37 : 32. Body- 

 chamber of moderate size, about one-fourth the length of the shell ; edge of the 

 aperture undulating ; below it on the cast there is a well-defined shallow, crescentic 

 dej)ression, which at each extremity of the longer axis of the shell is 10 mm. 

 below the edge of the aperture, from whence it passes down and forms a shallow 

 sinus on the broader aspect of the shell. Septa deeply concave, horizontal, 

 distant from each other about two-fifths of their own diameter. Siph uncle 

 cylindrical, about one-eighth the width of the shell ; nearly central. The surface 

 of the cast, where it is well preserved, shows admirably the fine " wrinkles " and 

 minute punctures described by the Brothers Sandberger under the name of 

 " Runzelschicht " ('Die Verstein. Nassau,' 1856), which have been ascribed to 

 the markings on the mantle of the animal preserved through the medium of the 

 extremely fine sediment which filled the body-chamber, and sometimes too the 

 septate parts of the shell after the death of the animal, but before the decay of 

 the soft parts. The ornaments in this specimen are very conspicuous ; they 

 consist of fine imbricating striae, disposed with great regularity, the edges of the 

 imbrications being directed towards the aperture. Four of them occupy the space 

 of 1 mm. ; they are therefore visible to the naked eye, at least in the older parts 

 of the shell (PL VIII, fig. 1 c, natural size, and giving nearly the number of 

 strias of the part figured). ■ 



Size. — The most complete specimen, wanting only a portion of the apical end, 

 measures 190 mm. in length, the diameter at theapertural extremity being 35 mm., 

 that at the apical one 13 mm. 



Affinities. — This species is closely related to Orthoceras Clanense, and the 

 question naturally arose as to whether it might not have been the young of that 

 form. There are, however, some points which weigh against this supposition : 

 chief among these is the rate of tapering, which is much quicker in 0. Clanense 

 (1:6) than in the present species (1:8); further, the septa in 0. Sollasi are 

 horizontal, while they are oblique in 0. Clanense. The ornaments, though 

 finer in 0. Sollasi than in the latter species, are the same in character in both, 



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