ORTHOCERAS PERAPPROXIMATUM. 11 



short. Sipliuncle central, cylindrical, rather wide, but scarcely increasing in 

 width between the septa. Test smooth. The largest example is 520 mm. in 

 length, in which measurement is included a small portion of the extreme apex, 

 which is broken off. The greatest diameter is 65 mm., the least 12 mm. 



Affinities. — This species may be distinguished from Orthoceras acre by its less 

 slender proportions and wider septa; from Orthoceras I'orteri by its slower rate of 

 tapering, and more distant and more horizontal septa. None of the Belgian 

 species make any near approach to the one here described. 



Remarks. — The interiors of the chambers of the specimens of which sections 

 have been made are filled with calc-spar, which has in some places distorted, and 

 in others destroyed the septa ; the siphuncle, however, is intact throughout the 

 whole length of the specimens examined. 



Locality. — Clane, county of Kildare. 



Orthoceras peeapproximatdm, A. H. Foard. Plate II, fig. 3. 



1896. Oethoceeas peeappeoximatijm, A. II. Foord. Ueber die Orthoceren des 



Kohlenkalks (Carboniferous Limestone) 

 von Irlaud. . . . Inaugural-Dis- 

 sertation zur Erlangung der Doktor- 

 wiirde . . . der Kgl. bayer. Ludwig- 

 Maximilians-Universitat zu Miincben, 

 p. 22. 



Description. — Shell very small, tapering at the rate of 1 : 5. Section circular. 

 Body-chamber about one-third of the length of the whole shell, therefore long. 

 Sejjta somewhat oblique, very numerous, about 2 mm. apart. Siphuncle 

 cylindrical, excentric. Test covered with extremely fine, thread-like lines. 



Size. — An example in which the greater part of the body-chamber is wanting 

 measures 75 mm. in length; the greatest diameter amounting to 16 mm., the 

 least to 3 mm. 



Affinities. — In its closely-set septa this species resembles Orthoceras ci/lin- 

 draceum, J. Fleming;^ it is, however, distinguished from the latter by its more 

 rapid rate of increase, the obliquity of its septa, and the excentricity of its 

 siphuncle. 



Remarks. — There is always a certain measure of doubt as to whether very 

 small specimens, such as those here under description, may not have been young 



^ ' Annala of Philosophy,' vol. v, Jan. — Juno, 1S15 ; ' Observations on the Orthoceratites of 

 Scotland,' p. 199, pi. sxii, fig. 3. See above, page 7. 



