PLEUROTOMARIA. 399 
335. PLEcROTOMARIA BLONGATA, Sowerby, 1818. (= Pl. mutabilis, Deslongchamps, 
pars.) Plate XXXIII, figs. 4, 5, 6, and 7; 
Plate XXXIV, fig. 8. 
1818. Trocuus ELoNGATUS, Sowerby. Min. Conch., pl. exciii, figs. 2 and 3. 
1854, PuevroromMarta ELoNGATA, Sowerby. Morris, Cat., p. 271. 
1873. — — — Tawney, Dundry Gasteropoda, p. 37 
(29). 
Syn. = MUTABILIS, Deslongchamps, vars. BLONGATA, MUTICA, and 
amBIeua. Mém. Soe. Linn. Norm., vol. 
viii (‘Les Pleurotomaires’’), p. 108, &e., 
pl. x, figs. 14 and 15; pl. xi, fig. 1. 
Bibliography, §c.—Since this is a group rather than a species, in the stricter 
acceptation of the term, it would be useless to attempt a fullsynonymy. Tawney 
included the following, with more or less doubt, under this heading, viz. Pl. 
abbreviata, Sowerby, Pl. conoidea, Deshayes, and Pl. Hbrayana, V@Orbigny. The 
above, together with other named forms, are doubtless connected, and may for the 
most part be regarded as varieties. Nevertheless Deslongchamps, who attached, 
little value to the spiral angle as a means for determining species in Plewrotomaria 
made his Pl. mutabilis a little too comprehensive. Since Sowerby originally 
recognised two species in this group, viz. Pl. elongata and Pl. abbreviata, I have 
concluded to follow his example. 
It will be observed in the sequel that Pl. elongata, as thus limited, covers a 
considerable variety of forms according to the horizon, the lower beds usually pre- 
senting the narrower forms, although in the Parkinsoni-zone at Burton Bradstock 
and elsewhere are a number of small specimens, many of which may be allotted to 
Pl. elongata in a general sense. 
General Description.—Shell conical-elongate, not umbilicated. Spire regular 
or slightly concave, the spiral angle ranging from about 40° to somewhat less 
than 50°. Whorls about twelve, excavated, and terminated by a basal rim which 
projects over each succeeding whorl and constitutes an important feature. This 
rim is crenulated in some cases, and subcrenulate to smooth in others, presenting 
considerable variety in its sculpture. The intercarinal spaces have rich spiral 
ornament, slightly reticulate in the earlier whorls, subgranulate in the later ones. 
The sinus-band is very anterior, rather narrow, and but slightly prominent, 
usually presenting one median spiral cross-hatched by growth lines, but in some 
cases the ornamentation is more complex. The body-whorl is angular at the 
periphery, with a flat base which is not as arule excavated ; base spirally grooved ; 
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