AET.8 CEUSTACEAISrS FEOM MEXICO EATHBU]Sr 3 



While the lobules of the carapace correspond generally to those of 

 SGulptus, there are above the posterior margin 2 lobules separated on 

 the median line, but in scidptus one continuous elevation. The form 

 of the abdomen and the ornamentation of the cheliped are similar 

 in the 2 species although the cheliped of mexicaims may be less rough. 



XANTHOSIA 3 AMERICANA, new species 



Plate 6, Figure 1 



Description. — A veiy small carapace embedded in a hard matrix. 

 Approximate length 3.4, width 6 mm. The fronto-orbital margin 

 is nearly as long as the middle width of the carapace excluding 

 spine ; the greater part appears to be occupied by the orbits ; there is 

 a stout lateral spine, broken off; j)ostero-lateral longer than antero- 

 lateral margin. Surface well areolated; summit of areoles 

 minutely granulated. Cardiac region nearly occupied by two 

 round areoles; mesogastric region narrowly constricted, almost 

 subdivided at middle, the anterior areole linear-oval, the pos- 

 terior areole narrow triangular, not wholly separated from the 

 roundish elevations at the posterior angles of the region; pro- 

 togastric lobes swollen but undivided ; three areoles crowded together 

 at the inner angle of the branchial region, the outermost one the 

 largest; in front of these an acute ridge runs across the branchial 

 region in an obliquely transverse direction from the protogastric 

 region to the lateral margin where it forms the axis of the large 

 lateral spine. Between the spine and the tooth at the outer angle 

 of the orbit there are two teeth on the antero-lateral margin. The 

 true postero-lateral margin is visible and shows four sinuses sep- 

 arated by shallow teeth, indicating the position of the ambulatory 

 legs. The details of front and orbit are not clear, but the orbit is 

 seemingly defined by the thickened outer angle of the front; two 

 closed orbital fissues. A low swelling is present behind each frontal 

 lobe. 



Occurrence. — Cortez pump station, Tepetate, 200 meters N. E. of 

 S. W. slope of hill ; altitude about 50 meters ; Oligocene ; November 

 17, 1920; Coll. No. M 23 V; holotype. Cat. No. 371098, U. S. N. M. 



Relation. — This species has the same general form as X. gibhosa 

 Bell,* the type species of the genus. It has the strong spine or pro- 

 tuberance at the lateral angle seen in X. granulosa (McCoy ).^ 



« Xanthosia is referred provisionally to Fam. Dynomenidae by Glaessner, Fossilium 

 Catalogus, 1, part 41, 1929, pp. 401 and 428. 



< Mono. Fossil Malac. Great Britain, part 2, London, 1SG2 (1863), p. 3, pi. 1, figs. 4-6. 

 Eldem, p. 4, pi. 1, fig. 13. 



