ORTHOCERAS CLANENSE. 21 



V. Group IlIBRICATA. 



Orthoceras Clanense, a. E. Foord. Plate VII, figs, a — g. 



1896. Ohthoceeas Claxense, A. S. Foord. Ueber die Orthocerea des Kohlen- 



kalks (Carboniferous Limestone) von Irland. 

 Inaugural-Dissertation Kgl. bayer. TJniversitat 

 Miinchen, p. 33. 



Description. — Shell moderately elongate, sti-aigbt; tapering at tlie rate of 

 about 1 : 6. Section circular in a fragment of a large adult shell, slightly elliptic 

 in a smaller one, the greater and lesser diameters in the latter being nearly 

 as 6 : 5. Body-chamber slightly fusiform, attaining nearly one-third of the length 

 of the shell ; outline of the aperture somewhat undulating, as is also the base of 

 the body-chamber. Septa distinctly oblique (PL VII, fig. 1 c), the sutures, as 

 seen on the cast of a shell of medium size, making an angle of about 10° with the 

 longitudinal axis of the shell. Chambers very concave, moderately deep, about 

 four times as wide as they are high. Siphuncle slightly excentric, beaded in the 

 young shell, as seen in a natural fracture of the apical part of a specimen 

 (PL VII, fig. 1 g), but tending to become cylindrical as the shell increases in 

 size. Test varying in thickness from '7^ mm. to 1*5 mm., the thickest part being 

 upon the body-chamber of the adult shell. Surface ornamented with multi- 

 tudinous, fine strise, imbricating upwards ; these are generally arranged with 

 great regularity over the surface of the test, this regularity being only here and 

 there a little disturbed by the strije being more crowded together. Thus, for the 

 most part, four of the stride may be counted in the space of 1 mm., but in some 

 places not more than two. But on the body-chamber of an adult shell the stria? 

 are 1 mm. apart. Towards the middle of the body-chamber of the adult shell the 

 striie become wider apart, and generally disappear before the aperture is reached, 

 leaving the shell quite smooth. 



Size. — The length of the most complete specimen is 255 mm., the body- 

 chamber being nearly perfect, but the apical part broken (PL VII, figs. 1 a, 1 b). 

 The greatest diameter of this specimen is 57 mm., the least 22 mm. A large 

 fragment collected measures 220 mm. in length, with a diameter at the posterior 

 end of 70 mm. and at the anterior end of 85 mm. This specimen consists of part 

 of the body-chamber and a few of the septa, with portions of the test attached. 

 It is in the Museum of Science and Art, Dublin. 



4 



