176 L. F. SpatJt — Notes on Ammonites. 



purposes than the shape of the aperture ". The presence or absence 

 of lateral lappets at the mouth- border is used for classification 

 by Mascki, 1 who put Parkinsonia and Strenoceras into the family 

 Otoitidse, Baculatoceras into Stemmatoceratidse, Garantiana and Sub- 

 parkinsonia into Stephanoceratidas. But Wetzel 2 has found ■' ears" 

 in a small form of Garantiana and only very slight lateral processes 

 in larger forms, and he thinks that probably — as is the case also in 

 Parkinsonia — in certain series the "ears" disappeared with age, 

 earlier in some series and later in others. Again, in JZecticoceras, 

 Glochiceras, and other Oppelids "ears" are often confined to the 

 younger stages, " vary in form and size from one specimen to another, 

 and show by this alone an impress of individuality that seems to 

 denvthem any usefulness for systematic purposes." 3 



When Waagen,in 1871, combined the Ammonitid genera in eight 

 groups, he attributed "great importance to the presence or absence of 

 the shell-plates termed Aptychus and Anaptychus, and to the 

 particular structure of these remains ".* Wright 5 also expressed the 

 opinion that " the Aptychus played an important part in the organic 

 functions of this large extinct group of tetrabranchiate Cephalopods". 

 But it had been shown long before that, in the case of Gastropods, as 

 the operculum sometimes varies in structure in species of the same 

 genus, as it is present in some volutes, cones, mitres, and olives, and 

 absent in other species of these genera, and as some genera in 

 a natural family, as Sarpa and Dolium among the Buccinoids are 

 without an operculum, whilst the other genera of the same family 

 possess that appendage, it obviously affords characters of very 

 secondary importance. 6 H. Douville 7 thought that " there was 

 nothing to show that in one and the same family one might not find 

 Aptychi of the same form that could have been either horny or else 

 more or less impregnated with calcareous matter, the former would 

 have disappeared during fossilization, at least in the majority of 

 cases, whereas the latter would be preserved. The absence of the 

 Aptychus might, therefore, be only apparent, and it was a character 

 of little importance". The assumption that the operculum of 

 Cephalopods has a greater systematic value than that of Gastropods, 

 even if not homologous, is not justified. Apart from this our scanty 

 knowledge of Aptychi found together with their parent Ammonites 

 has proved a great practical difficulty, and Waagen's classification 

 was, from this point of view, unsuccessful. 



Mr. Crick 8 thought that the traces of muscular attachment of the 



1 "Die Stephanoceras-Vervt&ndten der Coronatenschichten von Nord- 

 deutschl." : Dissertat., Gottingen, 1907. 



2 "Beitr. z. Pal. u. Stratigr. d. nordwestdeutschen Jura, ii, Faunistische 

 u. stratigr. Untersuch. d. Parkinsoni-iSckichten d. Teutoburger Waldes bei 

 Bichfeld " : Palseontographica, vol. lviii, p. 159, 1911. 



3 Wepfer, op. cit., p. 40. 



4 Zittel, History of Geology and Palceontology , English trans., 1901, p. 403. 



5 Op. cit., 1880, p. 176. 



6 E. Owen, Lectures on the Comparative Anatomy and Physiology of the 

 Invertebrate Animals, 1843, p. 296. 



7 " Cerat. de la Craie " : loc. cit., p. 278. 



s " On the Muscular Attachment of the Animal to its Shell in some Fossil 

 Cephalopoda (Ammonoidea) " : Trans. Linn. Soc, vol. vii, pt. iv, p. 109, 1898. 



