232 PEOF. p. M. DUNCAf's EEVISIOlSr OP THE 



regular ; the zones are nearly parallel ; interporiferous area 

 smaller than the poriferous zones ; the postero-lateral straight, 

 sunken, open, shorter where petaloid than the antero-lateral and 

 not so divergent, pores as in the other pair. 



Peristome excentric in front, slightly semilunar, but narrow 

 from before backwards and generally small ; a broad posterior 

 labrum. A narrow amphisternum, bounded by broad ambulacral 

 areas. The convex actinal surface with small interradial plates, 

 the right posterior interradium with abnormal (or ancient) hete- 

 ronomy, the second plates of zones a and 6 uniting. Periproct 

 elliptical at the upper part of the posterior truncation. 



A peripetalous fasciole following the general outline of the test, 

 and the anterior part of it double and with or without offshoots. 

 A very slender linear infra-anal fasciole extending from below the 

 periproct to the ambitus near the ambulacra. Horizontal sutures 

 often bare. Ambulacra bare on either side of a tuberculate 

 sternum ; tubercles uniform from the ambitus to the peripetalous 

 fasciole, larger above it and adjoining the petals. 



'Recent. China. One species, IB', chinensis, Gray. 



The subanal branch is not sufficient to modify the posterior 

 ambulacral plates, and does not bound a plastron. 



Genus Peeicosmiis, Agassiz, 1847 (subgenus), Catal. Bais., 

 Ann. d. Sci. Nat. ser. 3, vol. viii. p. 19. SerJclots, 1854, Java 

 Ech. pt. 4, p. 16. Desor, 1858, Synopsis, p. 396. McGoy, 

 1882, Frodr. Fal. Vict, dec, vii. pp. 15-21, pis. 64-68. 

 Duncan, 1887, Quart. Jo%irn. Geol. Soc. vol. xliii. p. 423. 



Test moderate to very large in size, thick, subcordiform, elon- 

 gate or short, tumid and depressed dorsally, with a well-marked 

 anterior groove, and more or less truncated posteriorly. 



Apical system subcentral, compact and small; number of 

 genital pores variable. 



Ambulacra diverse, the anterior in the groove with small pairs 

 of pores ; the antero-lateral divergent, long, sunken, the poste- 

 rior shorter and closer, pores unequal. 



Periproct large, excentric in front, labiate. Periproct ovaL 

 upon the posterior surface. Ornamentation small. 



A peripetalous fasciole circumscribing the petaloid parts of the 

 ambulacra, and a marginal fasciole passing all round the test, 

 sometimes slightly disconnected. 



Fossil. Upper Cretaceous (?). Eocene: Europe, N. Africa 

 Java. Miocene : Australia. 



