PROM THE CHLORITIC MARL. 235 



oblique, and nearly central ; the peristome entire and without auricles, and therefore 

 edentulous. A diagnostic character of the family is the periprocte, which is basal and 

 pyriform, about the same size as the peristome, and situated between the border and the 

 mouth. The tubercles are small and numerous, disposed in regular series, and raised upon 

 smooth circular elevations, with perforated summits ; in this we discover another 

 organic difference between the Echinonid^ and the EchinoconiDjE. The EcHiNONiDiE 

 inhabit the seas of the Antilles, the Philippines, the Trinity, Cuba, Zanzibar, and New 

 Zealand, and tests of the same species are found in a semi-fossil state in the calcareous 

 tufa of Guadeloupe, Cuba, and Porto-Rico. 



The fossil species are included in the genus Pyrina, which are all found in the different 

 stages of the Cretaceous rocks. 



Genus — Pyrina, Desmoulins, 1837. 

 Pykina, Globatek, and Nucleopygus, Agassiz, 1837. 



Test oval or round, depressed or globular, sometimes pentagonal or enlarged before and 

 narrow behind. Under surface inflated and often depressed around the mouth-opening, 

 which is oval, obhque, and inclined from the right to the left side ; this aperture is 

 nearly central, and destitute of lobes and auricles. The apical disc is small, compact, 

 and nearly central ; it is composed of four perforated genital plates, of which the right 

 antero-lateral is the largest, extending into the middle, and supporting the small niadre- 

 poriform body. The five small ocular plates are closely wedged into the angles formed 

 by the genitals, all the elements of the disc being soldered together. The vent is oval 

 and marginal, in general nearer the upper than the under surface. The poriferous zones 

 form straight equal narrow linear depressions, all composed of simple pores in regular 

 pairs extending from the peristome to the disc. The tubercles are mamniillated and 

 imperforate, larger at the under side, and the inter-tubercular surface of the plates is 

 covered with a great number of granules. 



Pyrina differs from EcJiinoconiis in having in general an elongated form, the apical 

 disc has only four genital plates, the mouth is oval, oblique and edentulous; the 

 vent is marginal, and the tubercles are imperforate, whereas in EcUinoconus the disc has 

 five genital plates, the mouth is circular or slightly pentagonal, and provided with denti- 

 ferous jaws ; the vent is basal or infra-marginal, and the tubercles are maramillated with 

 crenulated bosses and perforated summits. 



