XArTiLiPj:. 
GO 
close to the convex border. The shell is smooth. Found only in 
the Carboniferous Limestone of Belgium, Calcaires of Auseremme 
(Assise iii. e), of Furfooz (Assise iv. b), and of Panquys (Assise iv. 6), 
and at the same horizon in Ireland. It is said by de Koninck to 
be rare in aU the Belgium localities cited, and it is probably equally 
so in Ireland. Type, Gijroceras gibberosum, de Koninck h 
R<marl's. Professor Hyatt regards Ai 2 )ocenis gibberosum as 
closely related to Cgrtoceras J^erneuUlianum, de Kon.~, but he con- 
siders also that it is transitional to Sole nocheilus ( = Asgnipfoceras^ 
in the position of the siphuncle, the smoothness of the shell, and 
the compressed outline of the whorls. Ggroccras e.i'pansum, 
Saemann^ may belong also to the same group as Aipoceras gibbero- 
8inn. 
Gyroceras (Aipoceras) compressum, Foord. 
Sj). Char. Shell composed of one and a half volutions. The cur- 
vature is not quite regular, the mature part of the shell forming a 
proportionally lesser curvature than the earlier. The initial point 
is slightly obtuse, and bears no trace of a cicatrix ; it is inclined 
towards the dorsal side of the shell, and leaves a central opening of 
considerable size. At a little distance from tlie apex tlie section of 
the shell is obscurely oval, but at a later stage of growth it becomes 
subtri angular, and much higher than broad. Tlicre is a slight 
emargination in the superior border of the ai)erture. The septa are 
moderately distant from each other ; the sutures arc slightly con- 
cave at the sides of the shell, but without any sinus on the peri- 
phery. The siphuncle is not known. The bo<ly-chamber is very 
large, occupying about of the total length of the shell. Tlie sur- 
face of the test is quite smooth, there being nothing but a few 
irregular lines of growth upon it. The test is excessively thin. 
The specimen in the Collection (figure G) differs sufficiently from 
G. (A.) gibherosam^ de Kon., to warrant its separation from that 
species ; it is much less inflated, the periphery being so narrow as 
almost to form a keel. The ratio of the ventro-dorsal to the trans- 
verse diameter is as 19 : 29, while in de Koninck 's species it is as 
29 : 24. 
JlernarJ.f!. Only five exarajdes of the species arc recorded by 
de Koninck, who compares it with the Gijroceras expansinn of 
Saemann, to which he thinks it comes very near. 
^ Faiine du Calcaire Carbonifere de la Belgique (Ann. Mus. Roy. d’Hist. Nat. 
de Belgique, tom. v.), p. (». ^ Pnd. p. 3.5, pi. xxxiv. IT. 0, a-c. 
^ Pal aeon tographica, 1854, Band iii. p. 107, tab. xxi. iT. 2, a-c. 
