250 W. H. Sudleston — On the Yorkshire Oolites. 



Belations and Distribution. — This form may be regarded as the one 

 described and figured by Morris and Lycett from a specimen in the 

 Scarborough Limestone. It probably represents one of the varieties 

 of Melania scalariformis so characteristic of the Inferior Oolite of 

 Normandy, and may possibly be, in part, Cerithium muricaio- 

 costatiim, Miinst. 



It differs chiefly from the typical C. vetusta (Figs. 9 and 10) in 

 the decussating nodes on the posterior margin of the whorls. 



Fig. A represents the aperture of a variety of Melania scalari- 

 formis occurring in the Inferior Oolite of Bradford Abbas. The 

 slight groove or canal at the anterior extremity is scarcely consistent 

 with the notion of Chemnitzia. The Yorkshire specimens of the 

 vetusta-growp are not sufficiently well preserved to show for certain 

 whether this critical feature exists or not. 



20. — ? Cerithium muricato-costatum, Miinster, 1844. PL VI. Fig. 1 7. 



1844. Cerithium muricato-costatum, Miinst., Goldfuss, t. 173, fig. 12. 



1860. Cf. C. tortile, Heb. and Deslong. Foss. of Monti. Bellay, p. 39, pi. yI. fig. 1. 



Description. — Specimen from the Millepore Bed (zone 2). 

 Leckenby Collection. 



Length 13 mm. 



Width 3 ,, 



Shell elongate, narrow, subturrited. Apical whorls imperfect. 

 The six anterior whorls are in a good state of preservation, but the 

 base is concealed in matrix. The longitudinal costce are straight or 

 very slightly curved, and deeply and regularly decussated, so that 

 the sculpture on the ribs is highly granulated. 



Other specimens from the same bed are somewhat less elongate, 

 but with the same style of ornament. 



Belations and Distribution. — This shell seems to occupy an inter- 

 mediate position between Ch. vetusta, which has the rib wholly 

 unornamented, and Cerithium muricatum (Dogger variety), where the 

 longitudinal and spiral systems of ornament are almost of equal 

 strength. It should be regarded, I have little doubt, as a Cerithium, 

 but its relationship to the vetusta group, which many people also 

 would relegate to Cerithium, induces me to place it here for the 

 sake of comparison. 



The most characteristic specimens are found in the Millepore Bed, 

 but something very like it occurs on other horizons, even as high up 

 as the Lower Calcareous Grit, where the form referred to Cerithium 

 Bussiense, D'Orb., is not very dissimilar. It may be fairly admitted 

 that, where the ornamentation of the whorls is so modified by con- 

 ditions of fossilization, accurate specific distinction becomes almost 

 an impossibility. 



EXPLANATION OF PLATE VI. 



Fig. 1. Chemnitzia lineata, Sow. (? = Melania procera, Deslong.). Dogger, Blue 



Wyke. Leckenby Collection, a. Front view ; b. 



back view. 

 ,, 2. Ibid. Specimen showing an earlier stage. Dogger, Blue "Wyke. My 



Collection. 

 ,, 3. Ibid. Specimen showing a still earlier stage. Dogger, Blue Wyke. Bean 



Collection, British Museum. 



