﻿146 MR. B. S. BFCKMAN ON CERTAIN [Feb. 1905, 



Juraformation ' (1856) p. 372; figure of holotype — d'Orbigny, 

 < Pal. Franc. Terr. Jur. : Ceph.' (1845) pi. xcix, fig. 4 only. 



Alocolytoceras tjsniattjm (Pompeckj), 1896. (PI. XVI, figs. 1-2, 

 & text-fig. 6, p. 152.) 



1896. Lytoceras tceniatum,~Pom\}Qck], 'Beitrage zu einer Revision der Ammoniten 

 des Schwabischen Jura ' pt. ii, p. 164 & pi. xii, fig. 7. 

 = ? Lytoceras Wvighti, S. Buckman, 1888, ' Monogr. Inf. Ool. A mm.' (Pal. 

 Soc.) pt. ii, p. 44, footnote 2. 1 



11 em arks. — The specimen submitted by Mr. Thompson agrees 

 with the above-quoted figure of Dr. Pompeckj's species, so far as 

 comparison can be made ; but the example is deficient in the 

 umbilical whorls. The Northampton specimen shows, in the um- 

 bilicus of the side not depicted in the Plate, striae indicative 

 of the annulose stage ; Dr. Pompeckj's figure shows both this and 

 the Germaini-stRge. But the Northampton specimen does not 

 differ in shape from my Lytoceras Wrighti. Is, therefore, Pom- 

 peckj's species the same as mine ? or is it a case of homceomorphy ? 

 So far, these characters of the Germaini and annulose stages have 

 not been noted in my species. The specimens are large, and the 

 inner whorls seem to be particularly smooth. 



Dr. Pompeckj (op. cit. p. 171) has misread the position of Al. Wrighti 

 in the genetic series, when he thinks that it may be the same as his 

 Lytoceras dilucidum ; my L. sigaloen is the species which occupies 

 that position, so that the comparable species in the same stage of 

 development are L. dilucidum, Pomp. (? Oppel) and L. sigaloen ; 

 L. tceniatwn, Pompeckj, and L. Wrighti, respectively. Now, 

 according to Pompeckj's figures, there is considerable difference in 

 the ontogeny of his L. dilucidum and L. tceniatum—a, difference 

 which suggests that they really belong to separate genetic series. 

 That may be the explanation of the likeness of L. tceniatwn and 

 L. Wrighti : it may be a case of homceomorphy. To settle this, in 

 fact, before one can dogmatize on the identity of any smooth 

 catagenetio species, it is necessary to be well-informed concerning 

 their ontogeny. 



Locality and Horizon. — Spratton Ironstone Workings, Brix- 

 worth, near Northampton, in the Northampton Sands. 



Date.— Hemera scissi, presumably. Ammonites of the genera 

 Lioceras and Tmetoceras indicate that the Northampton Sands are of 

 this date ; and there is no evidence of any earlier date as yet. The 

 date of Al. Wrighti is hemera aalensis; in strata of that hemera I 

 have found it both in the Cotteswolds and on the Dorset coast. 

 Dr. Pompeckj quotes Al. tamiatum from ' Zone of Lyt. toridosum, 

 Br. Jura a Quenstedt.' (Op. cit. p. 166.) 



Pachtlytoceras aalenianum, sp. nov. (PI. XY, figs. 3 & 4, & 

 text-fig. 5, p. 152.) 



Description. — A Lytoceratoid like jurense, but with a smaller 



1 The type-figure is Lytoceras jurense, Wright- (11011 Zieten), ' Monogr. Lias 

 Amm.' (Pal. Sue.) 1884, pt. vii, pi. lxxix. 



