Vol. 51.] HTTRCHISONTA AND ITS ALLIES. 213 



created by De Koninck ' for shells having angular whorls, and the 

 sinual band situated on the angle : this band is also very narrow, 

 and is more or less crenulated, the mouth is polygonal. Kittl 2 

 enlarges this genus to include some species previously described as 

 Pleurotomaria, Mourlonia, and Baylea, and ho also divides it into 

 sections. He states that in the earlier stages of growth the whorls 

 are planospiral, with the exception of the Triton group. Pithodea 

 was established by De Koninck 3 for the reception of a large buccinoid 

 shell with a wide sinus in the outer lip, which is represented on the 

 whorls by a broad, flat band. The presence of this sinus and band 

 suggests a relationship to Murchisonia or Pleurotomaria, but De 

 Koninck considers that the extreme thinness of the test distin- 

 guishes it from those genera, and he places it among the Turbinido, 

 although it does not appear to have been nacreous like the shells of 

 that family. This feature separates it also from the typical Pleuro- 

 tomarice, of which genus Fischer 4 considers it a section. It seems 

 well for the present at any rate to include it in the family Pleuro- 

 tomariidae, placing it in proximity to Murchisonia, whose test was 

 probably not nacreous. 



The name Caliendrum 5 was given by Brown to a genus for the 

 reception of a large buccinoid shell, previously described by Phillips 

 as Buccinum vittatum. He notes the broad, flat band on the middle 

 of the whorls, but does not observe the deep sinus in the outer lip, 

 the successive filling-up of which gives rise to the formation of this 

 band. Later palaeontologists have since referred this shell to the 

 genus Murchisonia, from the type of which it differs in having a 

 shorter spire, smooth, rounded whorls, and a flat sinual band bounded 

 by grooves. It agrees with the section Hormotoma in its smooth, 

 convex whorls, but differs in being less elongated, in having ventri- 

 cose whorls, and in the mouth being oval instead of circular. It 

 also bears a great resemblance to PiJiodea, but is devoid of the lines 

 and grooves with which that genus is ornamented. 



These sections cannot all be regarded of the same importance ; 

 Cerithioides, Pithodea, and Caliendrum, for instance, show a greater 

 divergence from the type than Hypergonia and Qlyphodeta. At 

 present they can only be considered as provisional, and their exact 

 value can hardly be determined until the whole series of Murchisonoid 

 shells occurring in the rocks from the Cambrian to the Trias is revised. 

 The data on which to found sections are in many cases very meagre, 

 few shells being really well preserved, and the mouth and nucleus are 

 often unknown, so that undue weight is frequently attached to the 

 form of the sinual band, the nature of the ornamentation, and the 

 size. Much importance cannot be ascribed to the latter peculiarity, as 

 a single species varies considerably in this respect. The specimens 



1 Annales Mus. Roy. Hist. Nat. Belgique, 'Faune du Calc. Oarb. de la 

 Belgique,' vol. viii. (1883) pt. iv. p. 64. 



2 ' Die Gastropoden der Scbichten von St. Cassian, etc' p. 181. 

 8 Op. supra cit. vol. vi. (1881) pt. iii. p. 88. 



* Man. de Couch. 1887, p. 850. 



5 ' Illustr. Fuss. Couchol. Great Britain & Ireland,.' 1840, p. 52. 



