270 PLIOCENE MOLLUSCA. 



very clearly sculptured; spire elongate, regularly tapering; apex small, rounded; 

 suture deep ; mouth ovate with a well-marked labial sinus below the suture ; outer 

 lip thin, curved, slightly expanded, continuous with a short and open canal. 



Dimensions. — L. 14 mm. B. 5 mm. 



Distribution. — Not known living. 



Fossil: Coralline Crag: Sutton and Gedgrave (very rare), 

 Boyton. Waltonian : Walton-on-Naze, Beaumont, Little Oakley (very abundant). 

 Newbournian and Butleyan (passim, but not so common). Icenian : Postwick (fide 

 Wigham) ? Scaldisien : Antwerp. 



Bemnrks. — The name mitrula for the present species has been attributed to 

 Sowerby, but I think this is open to question. The shell described by him as 

 Buccinum, mitrula (Min. Conch., vol. iv, p. 103, tab. ccclxxv, fig. 3) seems to mo 

 different from that known to Wood, and since then to Crag geologists generally 

 under that name. In fact, Sowerby says it resembles in general form an Eocene 

 species, B. janceum, which he figures on the same page. His figures are, perhaps, 

 inaccurate, but they can hardly be in any case Wood's JR. mitruln , nor is it possible 

 to decide with certainty the species they are intended to represent. It seems 

 desirable, therefore, to drop the reference to Sowerby, and for the future to attri- 

 bute the present name to Wood. Wood's figures, though they have not the accu- 

 racy of a photograph, are meant no doubt for the present shell. Perhaps it should 

 Ije stated that the fossil Nyst figured in 1843 as P. mitrula was afterwards referred 

 by him to another species, so that Wood's name of 1848 has clearly the priority. 



li. mitrula seems to be known only from the Pliocene deposits of the Anglo- 

 Belgian basin. It occurs in extraordinary profusion in the Waltonian Crag. I 

 have found at least 1000 specimens at Oakley. Its abundance at this stage makes 

 its restricted range, both in time and space, the more remarkable. 



B. mitrula is a somewhat variable form, one variety, not so prevalent as the 

 type, being more slender, with an elongate spire. The species has a character 

 of its own, however, by which it may be easily recognised. The special and rather 

 distant transverse striation above referred to, which in full-grown specimens has 

 often been nearly or wholly obliterated, is not clearly and regularly cut as in some 

 other forms of Baiihitoma. 



The shell figured by Nyst in 1881 [op. cii.) as Plewrotonia costata seems to be of 

 the present species. 



Raphitoma striatula, sp. nov. Plate XXIX, fig. 26. 



1844. Pleurotoma striolata, Philippi, Enuni. Moll. Sitiliie, vol. ii, p. 168, pi. xxvi, fig. 7. 



1872-4. Pleurotoma striolata, S. V. Wood, Mon. Crag Moll., 1st Supj)!., pt. i, p. 46, 1872; pt. ii, p. 



179, add. pi., fig. 2. 

 1905. Raphitoma (Smithiella) costulatum striolatum, Kobelt, Icon, schalentrag. europ. Meeresconch., 



vol. iii, p. 38:J, pi. xcvii, fig. 18. 



