38 ME. J. CAETEK ON THE PALEONTOLOGY OP [Feb. 1898,- 



Eostrum broadly triangular, slightly prominent. Orbito-frontal 

 border equal to half the width of the carapace. Antero-lateral 

 border compressed to a thin marginal edge, which is divided into 

 three or four quadrate lobes by notches or clefts. Postero-lateral 

 border thickened, inclining inward, and rendering the posterior 

 border narrower than the orbito-frontal. Dorsal surface uniformly 

 covered by small granules — about four in a square millimetre. 

 Areolar tubercles not observable. Most of the normal regions of 

 both the cephalic and scapular areas are separately indicated : lateral 

 gastric lobes inflated; mesogastric lobe small; urogastric un- 

 defined; the pyriform epibranchials terminate in the lateral 

 angles ; in some specimens a linear, indistinctly defined, meso- 

 branchial extends obliquely forward and inward ; cardiac region 

 large, inflated : the metabranchials occupy the postero-lateral 

 two-fifths of the scapular area. A sharp impression occurs in 

 the sinus between the anterior cardiac and the branchial lobes. 

 Pterygostomate region granulated like the dorsal surface. Sternum 

 moderately wide, lanceolate. Episternum sharplj- retroflexed, 

 acutely pointed. Epistome granulated; cavities for insertion of 

 external antennae large. Endostome large, with a median, and 

 oblique lateral, ridges. Orbits large, transversely oval, rather less 

 than two diameters apart ; two notches in both the upper and 

 lower margins. Ophthalmic peduncles constricted, granulated. 

 Buccal opening rather widened in front. Exopodite of external 

 maxillipeds a third of the width of the endopodite, which latter is 

 longitudinally furrowed and granulated. 



Pemale abdomen seven-jointed ; penultimate segment quadrate ; 

 telson triangular. 



Width of carapace = 10 to 30 mm. ; average adult width = 

 28 mm. ; average length =15 mm. 



Remarks. — In his generic diagnosis Bell quotes emargination of 

 the orbito-frontal border as a character ; but the frontal border of 

 the specimen which he has described and figured is imperfect, and 

 is made to appear emarginate by the accidental fracture of the 

 rostrum. Specimens in which this border is well preserved show 

 a slightly prominent, but distinct, rostrum. 



Affinities. — This species may be readily distinguished from its 

 allies by the depressed form of the carapace, by the trenchant 

 antero-lateral border, and by the uniformity in size and regularity 

 of disposition of the surface-granules. 



Distrihution. — Cambridge Greensand. Upper Greensand, War- 

 minster {fide Milne-Edwards). A single example from the Gault 

 near Aylesford is in the British Museum (No. 44311). I have 

 examined upwards of fifty specimens in the Woodwardian Museum ,- 

 the British Museum, the Museum, of Practical Geology, the York 

 Museum, etc. 



Xanthosia similis (BeU). (PL II, fig. 9.) 



1863. Mtyus similis. Bell, Monogr. pt. ii, pp. 6, 39 & pi. i, fig. 12, pi. xi, fig. 15. 

 1865. Milne-Edwards, Ann. Sci. Nat. ser, 5, vol. iii, p. 347 & pi. vi, fig. 7. 



Description. — The carapace is almost identical in character with^ 



