NArTLLTD^. 
59 
Gyroceras Eifelense^ cVArchiac aud de Verueiiil, sp. 
Isd:?. Spirula co^tata, Goldfuss (Bouii Museum), iu vou Becheiis 
Ilandb. der Geogiiosie vou II. T. de la Beclie, p. 530 G. b. 
Sandberger). 
1641. Cyrtocera-s nautiloideum, Phillips, Pal. Foss, of Cormvall, 
Devon aud West Somerset, p. 110, pi. xlvi. f. '220. 
164:?. Cyrthoceratites Eifelensis, d’Archiae X: de Yenieuil, Trans. Geol. 
Soc. 2nd ser. vol. vi. pt. ii. p. 349, pi. xxxi. ft'. 2, 2a, 2 b. 
1640. Spirula Eifeliemis, Quenstedt, Petrefactenkunde Deutschl. 
Band i. Abth. i. p. 49. 
1640. Gxjroceras nautiloideus, d’Orbigny, Prodr. de Paleont. Stratigr. 
vol. i. p. 52. 
1849. Gyroceras Eifelensis, d’Orbi<ruy, ibid. 
1852. Gyroceras Eifelense^ Giebel, Fauna der Vorwelt, Baud iii. Abth. i. 
p. 103. 
1650. Gyroceras costatum, G. & F. Sandberger, Die Yerstein. Nassau, 
p. 130, Taf. xii. ft. 5 a to 5 d (lig. 5 a is copied from d’Archiac aud 
de Yerneuil). 
Sp. Char. Shell coiled, forming at least one volution and a half, 
depressed vertically and increasing rapidly in diameter. Transverse 
section elliptical, the ratio of the two diameters being as 22 : 34 in 
an example which is a little crushed vertically, so that the lesser 
diameter is reduced ; the ratios of a specimen figured by d’Archiac 
and de Yerneuil (/or. cit.) are as 18 : 27. The septa are rather 
numerous, being 3 lines apart where the shell has a diameter of 
about 30 lines ; arching slightly forwards upon the periphery, 
otherwise straight. The increase in diameter is in the ratio of 1 to 
2-J in about ^ of a volution. The siphuncle is situated close to the 
convex border of the shell, in the median line ; it is cylindrical and 
of small dimensions. The ornaments of the test, upon the internal 
aspect of the shell, consist of “ from twelve to fourteen longitudinal 
folds or threads, vt ith pretty equal spaces. Transverse folds, arched 
from back to front, with wider spaces than the threads, pass over 
these latter, and form little tubercles upon them.’’ The external or 
ventral region of the shell is more ventricose than the dorsal, and is 
separated from it by two lateral ridges or keels. “ On each side of 
the back [<’. e. ventral side of the shell] ma}’ be reckoned seven 
rounded folds or threads, more prominent than those of the ventral 
[i. e. dorsal side] region. Transverse folds setting off from the 
lateral angles, where they join those of the inner part by a very 
salient tubercular pinching (pincement), turn back, forming a very 
elongated S, and describe upon the middle of the back a sinus whose 
concavity is turned forward. The passage of these folds over the 
