330 
SUPPLEMENT. 
along the median line of the dorsal aspect of the shell there is 
a narrow impressed zone, upon which there are four fine longitu- 
dinal ridges. This zone is coincident with the narrow dorsal sinus 
formed by the arching forward of the septa in the direction of the 
aperture. A portion of the test remains upon one of the specimens, 
and it appears to be perfectly smooth, as stated by Billings. 
The species to which J. Murrayi is most nearly related is the 
Orthoceras triangular e of d’Archiac and de Yerneuil, described below; 
but the latter has transverse ridges in the young shell, which swell 
into nodose prominences upon the dorsal ridge, and the siphuncle is 
filled with radiating deposits. In the subtriangular shape of the 
shell, the position of the siphuncle, and the character of the septa 
the two species agree perfectly, and their relationship cannot be 
doubted h 
Horizon. Trenton Formation (= Bala Limestone Group). 
Locality. St. Joseph’s Island, Lake Huron. 
Eepresented in the Collection by some fine examples presented 
by Dr. J. J. Bigsby, F.E.S., and a small specimen which was trans- 
ferred from the Museum of Practical Geology. 
Jovellania triangularis, d’Archiac & de Yerneuil, sp. 
1842. Orthoceratites triangularis, d’Archiac &; de Yerneuil, Trans. 
Geol. Soc. ser. 2, vol. vi. p. 347, pi. xxvii. ff. 1, 1 a. 
1856. Orthoceras triangulare, G. & F. Sandberger, Die Yerstein. 
Nassau, p. 155, Taf. xvi. 
1866. Orthoceras triangulare, Roemer, Beitr. zur geol. Kenntn. des 
nordwestl. Harzgeb. Abth. v. p. 4, tab. xxxiii. fF. 2, a-h. 
1874. Orthoceras triangulare, Barrande, Syst. Sil. de la Boheme, vol. ii. 
Texte hi. p. 104. 
1878. Orthoceras triangulare, Kayser, “ Die Fauna des altesten Devon- 
Ablagerungen des Harzes,” in Abhandl. zur geol. Specialkarte von 
Preussen, Band ii. Heft iv. p. 66, Taf. ix. fi’. 2, a, 6, f. 3 ? 
1884. Orthoceras ? triangulare, Kayser, Jahrb. der Konigl. Preuss. geol. 
Landesanst. und Bergakad. f. d. Jahr 1883, p. 15. 
\_Not 1843. Orthoceras triangulare, Portlock, Rep. on the Geol. of 
Londonderry, p. 375, fF. 3, «-c.] 
/Sp. Char. “ Shell in the form of an extremely elongated trian- 
gular pyramid, of which the section is a rectangular isosceles 
triangle with rounded angles, whose two smaller sides are curvi- 
linear, but the larger or hypothenuse is straight, whence it results 
^ Cf. the above figures of J. Murrayi with those of Orth, triangulare, G. & F. 
Sandberger, Yerstein. Nassau, Atlas, Taf. xvi. 
