238 PYRINA 



Diagnosis. — Test small, inflated, depressed at the upper surface. Ambitus elliptical,, 

 base flattened, margin much inflated ; mouth irregular, pentagonal, oblique, situated in 

 the middle of the base ; posterior border sulcated, vent elliptical, elevated near the upper 

 surface, plates closely covered with small tubercles. 



Dimensions. — Antero-posterior diameter four tenths of an inch ; height three tenths of 

 an inch. 



Descriptions. — The test of this rare little Tyrina is oblong-oval, inflated, rounded 

 before, and sulcated behind, for lodging the vent. In its longitudinal profile, fig. 3 d, the 

 test is higher behind than before, and always more or less truncated, the upper surface is 

 convex and slightly flattened, the under surface is convex and pulvinated, without a depres- 

 sion in the centre, the plates are covered with numerous small tubercles larger on the under 

 surface, the areas are excavated to receive the boss, which carries a small perforated 

 tubercle, fig. 3 g and h. The apical disc is small, composed of four perforated ovarial 

 plates and five very minute oculars, fig. 3/. The mouth opening is situated in the 

 middle of the base, fig. 3 c, and forms an irregular pentagon with its long axis oblique. The 

 vent is oval, situated in a sulcus high up in the posterior border, and the periprocte is much 

 nearer the upper than the under surface, fig. 3 h, and fig. 3 e. The poriferous zones 

 are extremely narrow, and appear like fine depressed lines on the surface of the shell. 



Affinities and Differences. — This species differs from Pyrina Desmoulinsii in having 

 the posterior border sulcated for the vent which occupies a higher position in this 

 Urchin. 



Locality and Stratigraphical Position. — It is said to have been collected from the 

 lower chalk of Dorsetshire. In France M. Cotteau records it from I'fitage Senonien, he 

 collected it in that formation at Saint Christophe, and at Tours, Indre-et-Loire, and at 

 Villedieu, Loir-et-Cher. 



Pyrina l^vis, Agassis, 1840. PI. LIV, fig. 1 a — e. 



Galerites l^vis, Agassiz. Cat. Syst., p. 7, 1840. 



— — Besor. Monographic des Galerites, p. 24, pi. iv, figs. 8 — 11,1843. 



— — Agassi:. Cat. rais., p. 91, Module 79, 1847. 



— — (VOrbigmj. Prodrome, t. ii, p. 272, 1847. 

 EcHiNOCONUs — d'Orbigny. Revue Zoologique, p. 21, 1854. 



Pykina — Cotteau. Paleontol. Francaise, t. vi, p. 490, pi. 987, figs. 6 — 9, 



1855. 



Diagnosis. — Test subpentagonal, enlarged anteriorly and contracted posteriorly, 



