ORTHOCERAS SANCTI-DOULAGHI. 5 



in some places with the siphuncle. The septa are otherwise well preserved. 

 Their short " necks" are easily seen in longitudinal sections, a slight expansion of 

 the siphuncle marking their termination (PI. Ill, fig. 1 d). The siphuncle is 

 slightly excentric and of moderate breadth, being about 4 mm. in diameter, or 

 about one-eighth of the diameter of the shell. This proportion, however, would 

 be reduced were the shell uncompressed. The surface of the test is quite smooth. 



Size. — The largest example is 520 mm. in length, with an apertural diameter of 

 70 mm., the apical diameter (almost the extreme apex) being only b mm. 



Affinities. — This species bears some resemblance to Orthoceras fandum, de 

 Kon., but the septa are wider apart, and the rate of tapering is slower. The 

 specimen figui-ed by de Koniuck,^ which I examined when in Brussels in 1893, 

 consists of jjarts of two individuals, the body-chamber not belonging to the same 

 one as the septate part. From Orthoceras Colei the present species is distinguished 

 by its slower rate of tapering and more nearly central siphuncle. 



BemarJiS. — This species is represented by two fine specimens, one of which is 

 nearly complete, wanting only a small part of the apical end. The septa and 

 siphuncle are well preserved in both individuals, though the spaces between the 

 septa are filled with crystalline calcite. Some of the septa are pushed out of 

 shape by rock pressure against the walls of the shell. 



I have named this species after Mr. J. Nolan, of the Geological Survey of 

 Ireland, to whom I am much indebted for the kind help he has rendered me 

 in giving me access to works I'elating to the literature of the subject of this 

 Monograph. 



Locality. — Clane, county of Kildare. 



Orthoceras Sancti-Dimilaghi, A. H. Foord. Plate I, figs. 3 a — e. 



ISOG. OiiTiiocERA^ Sanx'Ti-Doulaoiii, a. H. Foord. Ueber die Orthoceren des 



Kohleukalks (Carboniferous Limestone) 

 von Irland. . . . Inaugur-al-Disser- 

 tiition zur Erlangung der Doktorwiirdi' 

 . . del- Kgl. bayer. Ludwig-Maxi- 

 niilians-Universitiit zu Miinclien, p. 17. 



Description. — Shell elongate, tapering at the rate of 1 : 9. Section circular 

 when uncompressed. Body-chamber of moderate length, l)nt its proportion to 

 the whole length of the shell cannot be ascertained in any of tlie specimens 

 collected, as there is none perfect enough to supply the necessary data. The 



1 ' Calc. Carb. Belg..' 1S80, pt. ii, p. 05, pi. xlii, fig. 1. 



