The Quarterly journal of the Geological Society of London . ructure extending from the end of the siphon to the inner wallof the The prosiphon of JSgoceras latcecostaresembles the second type described by Grandjean, consisting < fone long bandelette, thus differing from JE. planicosta, in whichit is relatively short. Shell-development proceeds normally, and, until jE. Jatceeostaattains a diameter of over a millimetre, it is scarcely to be distin-guished from other voung capricorns. At a diameter of 4 mm.(PI. XXIII, fig. 4a) the whorl height of M. Jatceeosta is less than 1 Miner
The Quarterly journal of the Geological Society of London . ructure extending from the end of the siphon to the inner wallof the The prosiphon of JSgoceras latcecostaresembles the second type described by Grandjean, consisting < fone long bandelette, thus differing from JE. planicosta, in whichit is relatively short. Shell-development proceeds normally, and, until jE. Jatceeostaattains a diameter of over a millimetre, it is scarcely to be distin-guished from other voung capricorns. At a diameter of 4 mm.(PI. XXIII, fig. 4a) the whorl height of M. Jatceeosta is less than 1 Mineral Conchology vol. vi (1829) pi. dlvi, fig. 1. 2 F. Grandjean. Le Siphon des Ammonites, &c. Bull. Soc. Gcol. France,ser. 4, vol. x (1910) p. 49G. 274 DR. A. E. TRUEMAlSr ON THE [vol. lxxiv, the whorl height of the capricorns of Amblycoceras and Oistocerasat the same diameter; the whorl shape, however, does not differmarkedly from that of Liparoceras sparsicosta until the diameter Fig. 5.—Sutural development of iEgoceraslatrecosta (Soiverby). h50 9 mm. f 7 mm. e4-5 mm. d3*5 mm. c0-7 mm. b a [a-g, W. D. Lang Coll. (figured in PL XXIII, fig. 4).h=Specimen figured in PI. XXIII, fig. 3 : W. D. Lang Coll. No. 1566.] of 10 mm. is reached, when JEgoceras latcscosta is less folds appear at a diameter of 35 mm.; but there are no ribson the periphery until the shell is nearly twice that size, onlybecoming fairly prominent at a diameter of 11 mm. )iameter. Whorl height. Whorl thickness. Umbilicu mm. per cent. per cent. per «cut •84 43 79 20 1-2 40 67 32 25 40 68 ?40 . 42 35 67 52 8-0 35 50 4o 14-0 29 36 46 The early sutures of the Capricorn forms are similar; indeed, the part 4] EVOLUTION OF THE LILAROCERATIDjE. 275 sutures from the third to the tenth are almost identical in eachspecies, the second suture having a ventral lobe which becomesdivided by a minute median saddle in the next suture (text-fig. 5 c,p. 274). The first signs of denticulations appear in JEqocer
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