﻿144 ME. S. S. BUCKMAN ON CERTAIN [Feb. I905, 



to give to torulosum and its smooth derivatives a new generic 

 designation ; and the three genera may be compared as follows : — 



Pietjbolytoceeas, Hyatt. Characterized by peripheral compres- 

 sion making the whorl-section triangular, which character 

 is developed even in the costate stage. 



Species : — Stage 1. A. hircinus (Schlotheim) (Quenstedt). 

 Stage 2. A. Leckenhyi, Lycett ; A. hircicornis, Schlcenbach. 



Apparently this series does not progress to the further (levi- 

 gate) stage. 



Alocolttoceeas, Hyatt. Peripheral compression slight ; whorls 

 passing from round to oval, to elliptical in the costate 

 stage, to compressed elliptical in the smooth stage. 

 Species : — Stage 1. Lytoceras coarctation, Pompeckj ; A. Ger- 

 main?, d'Orbigny. Stage 2? AX. Pompeckji, nom. nov. 

 (see below, p. 145). Stage 3. Lytoceras diliicidum (Oppel), 

 Pompeckj. Stage 4. Lytoceras sigaloen, S. Buckm. ; L. 

 Wrighti, S. Buckm. ; L. tceniatum, Pompeckj (Stages 2, 3, 

 in inner whorls). 



Pachtlttoceeas, gen. nov. (torulosum-group). 1 No triangularity, 

 no peripheral compression; but, rather, whorls somewhat 

 inflated towards the periphery. Whorls round in the costate 

 stage, to stout oval in the levigate. Genotype, A. torulosus, 

 Zieten. 

 Species : — Stages 1, 2. A. torulosus, Zieten. Stage 4. A.juren- 

 sis, Zieten ; P. aalenianum, sp. nov., with stage 2 in inner 

 whorls (see below, p. 146). Stage 5. P. phyttoceratoides, 

 sp. nov. (see below, p. 147). 



So there are, in these genetic series, as morphic equivalents 

 distinguished by their whorl-shape : in Stage 1, PI. hircinum, Al. 

 Germaini, P. torulosum (young) ; in Stage 2, PI. Leckenhyi, 

 P. torulosum (adult) ; in Stage 4, Al. sigaloen, Al. Wrighti, and 

 P, jurense, P. aalenianum, respectively ; while in Stage 5 there is 

 no morphic equivalent to P. phylloceratoides. Stage 2, or the 

 corrugate stage, seems to be particularly well-developed in two 

 series, and the contrast between Pleurolytoceras Leckenhyi and 

 Pachylytoceras torulosum is especially marked ; but in Alocolytoceras 

 this stage does not seem to be developed in a noticeable manner — 

 the species presumably to be reckoned to it is Al. Pompeckji. If 

 there is this difference in development, it will be a still more im- 

 portant distinction between Alocolytoceras and Pachylytoceras. 



In these genera the lobe-lines are of very similar pattern : the 

 saddles retain much of the primitive phylloid character, the lobes 

 are wide-stemmed, and not spreading, while they lack the high 

 development of the typical Lytoceras-lobes. For further remarks 

 on these lobes, see p. 151. 



1 Ilaxvs, stout. - 



