144 
NAUTILOIDEA. 
1860. Endoceras vertebrate, Eicliwald, Letliaea Rossica, vol. i. Seconde 
Section de Tancienne Periode, p. 1237, pi. xlyi. ff. 4, a, b, 5, & 6, a, b. 
Sj). Char. Shell straight, very long, elliptical in section. Rate 
of increase rather rapid, that is to say about 1 in 7. Septa 
numerous, distant about f the diameter of the shell. Siph uncle 
marginal, its diameter about J that of the shell. Surface of test 
unknown. 
Bemarlcs. A crushed and distorted specimen in the Collection may 
belong to this species. It is not so decidedly elliptical in section as 
Eichwald’s species, and its rate of tapering is not so rapid, but the 
distorted condition of the specimen re vents accurate measurement. 
Horizon. Orthoceras-Lime^ioTiQ ( = Arenig). 
Locality. Russia. 
Represented by two specimens, one being a polished section. 
Endoceras incognitum, Schroder. 
? 1869. Orthoceras commune, Karsten, Die Verst, des Uebergangsge- 
birges in den Gerollen der Herzogthiimer Schleswig imd Holstein, 
p. 50, tab. xvii. ff. 6, a, h. 
1880. Orthoceras speciei Angelin-Lindstrom, Fragmenta 
Silurica, p. 2, tab. iv. f. 16. 
1881. Endoceras incognitum, Schroder, Schrift. der physikal.-okonom. 
Gesell. zu Konigsberg, Abth. i. p. 86, Taf. iv. ff. 1 & 2 a-d. 
Sp. Char. Shell straight. Rate of increase about 1 in 8. Sec- 
tion circular. Septa approximate, distant from each other about ^ 
the diameter of the shell. Siphuncle marginal, its diameter about 
■| that of the shell. Surface of the shell perfectly smooth. 
Bemarlcs. At the end of the description of “ Orthoceras duplex ” 
by Angelin-Lindstrdm {loc. cit. p. 2), we read, “ In tabula iv. figura 16 
depictum est Orthoceras speciei indeterminati, form inter praece- 
dentes [viz. ‘ 0. commune ’ and ‘ 0. duplex ’] intermedium, concame- 
rationibus approximatis 0. duplicis et siphone 0. communis.” 
Upon this diagnosis and the figure accompanying it, Schroder has 
founded his species. He Says that E. incognitum has often been 
described under Endoceras duplex, and that it is very difficult to 
judge from the figures which of the two species is intended. The 
peculiar character of E. incognitum, he continues, lies in the position 
of the transverse ridges and furrows upon the siphuncle. A better 
way of distinguishing the two species is by a comparison of the septa, 
which in E. incognitum are much closer together than they are in 
E, duplex \E. Wahlenhergi]. 
