ENDOCERATTDJi:. 
137 
1875. Orthoceraa duplex, Mallada, Bol. Com. Mapa Geol. Espafia, 
tomo ii. p. 24. 
1876. Orthoceras duplex, lloemer, Lethma Geognostica, Theil i. Leth. 
Paljeoz. Atlas, Taf. vi. f. 2, a, h. 
1880. Orthoceras duplex, Angelin-Lindstrom, Fragm. Silurica, p. 1, 
tab. iii. ff. 9-11. 
1881. Undoceras duplex, Schroder, Schriften der physikalisch-okono- 
mischen Gesell. zu Kouigsberg, Jahrg. xxii. Abth. i. p. 82, Taf. iii. 
ff. 1, A, B. 
1882. Endoceras cf. duplex, Barrois, Terr, anciens des Asturies et de la 
Galice, p. 187, pi. iv. ff. 7, a, h, c. 
1885. Orthoceras (Endoceras) duplex, Roemer, Lethma erratica, in 
Dames and Kayser’s Palaeontologische Abhandl. Band ii. Heft v. 
p. 38, Taf. ii. ff 2, a, b. 
1887. Endoceras Wahlenhergi, Foord, Ann. & Mag. Nat. Hist. ser. 5, 
Tol. XX. p. 393, ff. 1, a-e. 
Sp. Char. Shell straight, very long. Tapering rather slowly at the 
rate of about 1 in 12, taking the average measurement of three adult 
specimens. Section circular. Complete body-chamber unknown. 
Septa moderately distant, that is, about 8 lines apart where the 
diameter is 2| inches, decreasing to a distance of 3 lines at a 
diameter of 8 lines. The distance of the septa varies considerably in 
different specimens, and even in different parts of the same individual. 
Thus in one measured the septa are 6 lines apart at a place where 
the diameter is 16 lines, while they are only 4 lines distant where 
the diameter has increased to 19 lines. But on the whole the septa 
increase their distance as the individual advances in age. Siphunclo 
proportionately larger in the young than in the adult, as is frequently 
the case in the testaceous Cephalopods ; that is to say, it attains to 
nearly half the diameter in the young shell (fig. 14, d), while in the 
adult it measures only about one third the diameter (fig. 14, c). Test 
consisting apparently of two layers ; the inner one being perfectly 
smooth and polished, whilst the outer, the surface of which is rarely 
preserved, is ornamented with transverse, irregular, slightly oblique 
riblets (fig. 14, h). 
Remarks. The “ Orthoceras commune ” of Boll (not Hisinger), 
which I believe to be identical with Endoceras Wahlenhergi, is de- 
scribed by that author as having the shell in well-preserved 
examples marked with obscure lines of growth, and in badly pre- 
served ones these are so eroded that their sculpture can scarcely be 
recognized : ” the latter is unfortunately the condition of most of the 
specimens in the National Collection. 
It has been a matter of great difficulty to me to select out of the 
numerous and divergent forms, described and figured by various 
