GASTEROPODA. 27 



and retains only the faintest traces of tubercles ; the axial umbilicus is very conspicuous ; 

 and all trace of the wide basal notch being lost, the aperture resembles an entire- 

 mouthed shell. The hard limestone being much used for rough walls, it is upon these, 

 when partial disintegration has taken place, that the casts of Purpuroidea are to be found. 

 The genus has never been discovered lower than the planking. 



PURPUROIDEA MOREAUSIA. Plate IV, figs. 1, la, 2, 3, 3a, 4. 



PURPURA MOHEAUSIA, Buviffnier. Mem. Soc. Philomath. Verdun, 1843, pi. 6, fig. 19, 



p. 26. 

 PUEPURINA D'Orb. Prod. Paleont., p. 357, 1850. 



P. Testa turritd, ylobosd ; spirdbrevi, anfractibus 3 4, nodulosis vel spiniferis ; spinis 

 magnis, obtusis, in serie unicd 7, 8, aut 9 in ambitu ; anfractu ultimo striato, striis regu- 

 laribus transverse subundulatis (obsolctis in (state senior f) ; aperturd ampld, subquadratd ; 

 canali dilatato, leviter excavato, 



Shell globose, spire prominent, whorls 3 4, angulated ; angles tuberculated ; tubercles 

 large, elevated, 8 or in others 7, upon a volution ; the last whorl ventricose ; the tubercles 

 increasing in size until they become large blunt spires ; beneath the tubercles the surface 

 has numerous undulating closely-arranged encircling costse; the aperture is large and 

 widely truncated at its base ; the inner lip is somewhat depressed in its middle part. 



This is by much the most abundant, and at the same time typical species of the genus. 

 There may be considered to be two varieties, one having 8, the other only 7, spines in a 

 volution ; the latter variety has the spire more depressed, the aperture occupying three 

 fourths of the entire length of the shell. The elevated longitudinal swellings, produced by 

 the successive extensions of the outer lip in growth, sometimes interfere with the continuity 

 of the encircling ribs, cause them to undulate, and occasionally obscure them altogether 

 hence, in the younger specimens, the ribs are more regular and distinctly marked. Very 

 rarely, indeed, individuals have been found which simulate P. nodulata, the lines of growth 

 being enlarged to imperfect ribs, which suddenly disappear, or are depressed at the place 

 where, in the species referred to, the second circle of nodules is situated ; the spire also 

 becomes more elevated, which adds to the resemblance. In the figure given by Buvignier, 

 the inner lip is more flattened, or Purpura like, than might have been expected ; but the 

 figure altogether is executed in a very indifferent manner. 



Locality. The vicinity of Minchinhampton is the only locality in which this remarkable 

 shell is known to have been procured in England. Buvignier mentions that M. Moreau, 

 of St. Mihiel, has found it in the Coral rag of that place, and likewise in the ferruginous 

 Oolite of Launoy. 



