292 ECHINOCORID^E. 



drawn by Mr. C. R. Bone for my late esteemed colleague Professor Edward Forbes, whose 

 accurate description I have adopted. They were collected from the Greensand of Black- 

 down in Devonshire, a formation whose geological horizon is probably about the junction 

 of the Gault and Upper Greensand, and I am not aware the species has been found in any 

 other locality. 



Family 13. — EcmNOCORiDiE, Wright, 1856. 



The Urchins of this family have an oval, cordate, or conoidal test, which often attains 

 a considerable size. 



The ambulacral areas are equal, narrowly lanceolate, and converge to one ambulacral 

 summit, which is always the vertex of the test. 



The poriferous zones are narrow, and the pores are disposed in pairs at some distance 

 apart. 



The surface of the plates of both areas has in general two horizontal rows of very 

 irregular, small, perforated tubercles, raised upon bosses with crenulated summits, and 

 having around their bases a circle of very small granules ; the entire surface of the plates 

 in some well-preserved tests is likewise covered with a profusion of similar microscopic 

 granulations. 



The mouth-opening is always placed near the anterior border ; it is transversely 

 oblong, and often bilabiate ; the vent is round, and opens either at the base, near the 

 margin, or in a supra-marginal region of the posterior border in different genera. 



The apical disc is usually narrow and much elongated ; it consists of four perforated 

 and one unperforated ovarial plate, with five perforated oculars : the whole of the 

 elements are well soldered together, and often covered over with a thin granulated layer 

 of the test, which conceals the sutures of the disc and converts the whole into a single 

 mass. In the genus Stenonia the apical disc is short and compact ; it is likewise small 

 in Holaster and Cardiaster, and large and elongated in Echinocorys. 



The cordate forms have an anteal sulcus feebly shown in Holaster, but largely developed 

 in Cardiaster, whilst in the conoidal forms, as Echinocorys and Stenonia, it is absent. In 

 the genus Cardiaster there is a marginal fasciole, which passes under the periprocte. 



The Echinocoridje are an extinct family of the cretaceous period, and the species are 

 distributed throughout all the rocks of this formation from the Neocomian strata up to 

 the beds of uppermost White Chalk. One living form which connects this family with 

 the Spatangid^e ought, perhaps, to be placed here, the genus Palaopneustes, Agassiz, 

 a singular Urchin which was dredged near Barbadoes by the Hassler expedition. 



