66 



Family Trochid^. 



Genus Troclius, Linnceits. 



Trochus (Scal.etrocuus) lindstromi, sp. nov. 



(PL viii., Figs. 1 and 2.) 



Sp. Char. — Shell p^-ramidal-conical, of more than six whorls, 

 with an acuminating sharp spire ; under surface flattened, not 

 concave, but depressed immediately around the columellar 

 centre, -which is quite devoid of an umbilicus ; whorls concave 

 or concavely-biangulate, close sutured ; body whorl with a 

 very sharp peripheral edge, dividing the upper superior from 

 the inferior surface of the shell, aperture transversely ovate ; 

 inner lip sharp, probably bevelled inwards ; surface ornamented 

 by obliquely-curved, somewhat rough and irregular, subimbri- 

 cating laminar striae. 



Obs — " It is with great diffidence the following species have 

 been described as belonging to the old genus Trochits. The 

 only reason for placing them there is the general exterior shape 

 of the shell, it having not been possible to find any evidences 

 from the microscopic structure of the shell nor from any traces 

 of a nacreous stratum or an operculum. On the other hand 

 there are so many genera of shells which have persisted from 

 the Silurian age through all the following and so still continue, 

 and it may therefore not be thought an impossibility that also 

 the Trochi existed already in the Silurian times." 



So writes Dr. G. Lindstrotn* on the Trochidse of the Wenlock 

 rocks of Gotland, but the union of the perforate and non-per- 

 forate fornrs made by this author, seems to me manifestly a 

 retrograde movement, more especially ^vhen several genera 

 have ali-eady been proposed for the reception of the perforate 

 Trochi, such, as Pala'otrocJius Hall, I!ot7'ochus 'Wh.it&eld, Flemingia 

 de Koninck, and probably Pycnom2jhali(,s, Lindst. The entire 

 absence of an umbilicus at once separates Trochus lindstromi 

 from all these genera, and places it more in accord with I'rochus 

 niloticus, Linn., I do not, however, feel at all satisfied that 

 this species, and its probable ally Euomphalus clarkei, de Kon.,f 

 from the Wenlock rocks of Yass can with certainty be referred 

 to Trochus. Indeed, the step-like outline of the whorls reminds 

 us of Meek's genus Omphalotrochiis, but this isumbilicate, like 

 the others mentioned above. On the whole it seems to me 

 that we have the indication of a further unrecognised genus, for 

 which I would suggest the provisional name of ScalcKtrochus.\ 



* Loc. cit., p. 145. 



t Kech. Foss. Pal. Nouv. Galles du Sud, 1870, Pt. 1, p. 41, t. 1, f. 7, 7a. 



X Scalse, a flight of steps. 



