XAUTILTD-r. 
73 
1>?44. Gyroceras aiyoceroSy de Koninck, Descrip, des Aiiim. Fossiles du 
Terr. Carb. de la Belgique, p. 53:?, pi. xlviii. IF. 1 u, 1 
1849. Xautiloceras aigoceros, d’Orbignv, Prodr. de Paleont. Stratigr. 
vol. i.p.ll2. 
1852. Gyroceras aigocetas, Giebel, Die Fauna der Vorwelt, Band iii. 
Abth. i. p. 193. 
1854. Xautiloceras aigoceras, Pictet, Traits de Paleont. vol. ii. p. 630, 
pi. 1. f. 8. 
1876. Gyroceras aigoceras, F. Poeiner, Lethrea Pahnozoica, Taf. xlvi. f. 3. 
1880. Gyroceras aigoceras, de Koninck, Faune du Calc. Carbonifere de 
la Belgique (Annales du Mus. Roy. d’llist. Nat. de Belgique, 
torn. V.), p. 8, pi. xxxii. tF. 4, 4 a, 4 h. 
1883. Trigonoceras paradoxicum (young), Hyatt, Proc. Boston Soc. 
Nat. Hist. vol. xxii. p. 291. 
Sp. Char. Shell discoid, com]^K)sed of two whorls, quite discon- 
nected. The initial point has not been seen. Section scutiform, 
the periphery hollowed out and bounded on each side by prominent 
ridges. The sides are compressed, slightly inflated in the middle, 
and narrowing to a sharp keel along the median line of the concave 
side. The body-chambpr appears to have occupied about g of the 
total length of the last whorl. The septa are numerous, their dis- 
tance from each other at the sides of the shell being about j of a 
line, where the diameter is 5 lines. The siphunclc is situated a 
little above the centre. The sides of the shell arc ornamented with 
transverse acute plications, from 38 to 40 in each whorl. These 
plications cease at the obtuse keels or ridges which bound the peri- 
pheral side of the shell, and are not continued upon the lattcT. 
The entire surface of the lest is covered with extremely fine longi- 
tudinal lines, which can only bo seen with the aid of a lens. 
Rnnarhs. The transverse ornaments and hollowness of the pori- 
j)hery in this .species give it a very characteristic aspect, and mark 
it off from the species of Gyroceras proper, with which it has been 
associated by do Koninck. Professor Jlyatt’s opinion, that T. aiyo~ 
ceras is only the young of T. jHiradoxicum , seems to rest upon tlie 
assumption that the latter was .similarly coiled throughout its whole 
length, whereas it has been seen that the coiling is only at the apex, 
and that the shell is afterwards but .slightly curved, a circumstance 
which has pro])ably led some authors to ])lace it (despite its very 
remarkable section) in the genus Cyrtoceras. 
Horizon. Calcscbistc de Tournai (Assise i. c) = Carboniferous 
Lime.stone. 
Locality, Tournai, Belgium. 
Fairly well represented in the Collection. 
