138 PEOF. p. M. DTJNCAT^'S REVISION OF THE 



broader tban long. Jaws exist. Perignathic girdle witli ambu- 

 lacral processes, discontinuous. Periproct very large or moderate, 

 placed between the apical system and the ambitus of the odd 

 interradium, and at some distance from this ; oblong, pyriform or 

 irregular in shape, flush ; may be in contact with the apical 

 system, or a portion of the posterior interradium may intervene. 

 Spines short and striated. 



Fossil. Oolites ; England, Europe. Cretaceous : Europe. 



In Pygaster megastoma, Wright, the periproct intrudes so 

 much, that the four basals are in a semicircle anteriorly, and the 

 madreporite is not central, but restricted to its normal basal -, 

 the posterior radial plates are widely separated. Probably it 

 should enter Galeropygus, Cott. 



G-enus Ptgasteides, Loven., 1887, Bih. till Kongl. Sv. Vet.-Ahad. 

 Handl. Bd. 13, Afd. iv. no, 10, p. 13. 

 Syn. Pygaster. 



The periproct is dorsal and posterior. 



Ambulacral plates all simple, the first plates broad, uniporous, 

 carrying distinct, separate auricles. Poriferous zones simple, 

 straight. Spheridia single. 



Interradial peristomial plates single and broad. Tubercles 

 perforate and crenulate, the primaries the largest. Ornamenta- 

 tion (epistroma) luxuriant. 



Recent. Caribbean Sea, near Virgin Islands, 200-300 fms. 



The species was founded by Loven upon one imperfect specimen 

 which only measured 3'5 niillim. in length and 2-16 in height. 

 But under the hands of the experienced teacher its structures 

 were described and admirably drawn. The uniporous ambulacra 

 and the solitary interradial plates at the peristome, coupled with 

 weak ambulacral perignathic processes and the anus close to the 

 apical system, characterize the genus, which Loven has placed 

 among the Echinoconidae, auct. It is a very aberrant form, and 

 the solitary specimen is defective. 



Section II. 



G-enus Discoidea, Klein, 1734 (Discoides), Nat. Disp. JEchin. 

 p. 26, pi. xiv. Gray, 1825, Ann. Phil. p. 429. Desor, 1842, 

 in Agassiz, Monogr. d'Ech. viv. etfoss. livr. 3, p. 50. Desor, 

 1858, Synopsis des Ecliin. foss. p. 175. Cotteau,18Qd, Ech. 



