1920] 



Kew: Cretaceous and Cenozoic Echinoidea 



141 



Belated forms. — This fonn resembles closely the Recent species 

 from the Gulf of California, Rhynchopijgus pacificus Agassiz, but 

 differs from the latter in being more narrowly elliptical in mar- 

 ginal outline ; is more acutely pointed in front than behind ; in that the 

 anal opening is elliptical in shape and not crescent-shaped; and in 

 that the petals are somewhat wider. 



Geologic horizon. — Occurs in a horizon probably equivalent to the 

 Gatun formation of the Gulf Coastal Plain, Lower Pliocene ( ?). 



Locality. — Oyster bank, East San Ysidro, Lower California, 

 Mexico. 



CASSIDULUS (EHYNCHOPYGUS) YNEZENSIS Kew, n. sp. 

 Plate 39, figures 2a, 2b, 2r, M 



IIolotijpe.—'No. 11345 Univ. Calif. Coll. Invert. Pal. 



Test small. ]\Ieasurements of holotype : anteroposterior diameter 

 25.6, transverse diameter 22.3 mm., greatest height 10.3 mm. Am- 

 bital outline broadly suboval, with the longitudinal diameter the 

 greater. Upper surface rises regularly to a rather high apex, which is 

 subcentral. Apical system eccentric to the anterior ; four large genital 

 pores present. Ambulacra subpetaloid ; petals of the bivium longer 

 than those of the trivium; the former wide open at the extremity, 

 the rows of pores converging and diverging very slightly in tlieir 

 distal ends ; anterior pair of petals wider than the posterior pair, due 

 to the greater width of the interporif erous area ; rows of pores diverge 

 and then converge in the distal end to form an elliptical-shaped petal ; 

 odd anterior petal aboiit one-lialf the widtli of the anterior paired 

 petals, and with the rows of pores not so convergent at the end of the 

 petal. Poriferous areas of all the petals narrow and of the same 

 width ; interporiferous areas of different widths, varying according 

 to the breadth of the petal. Actinal surface fiat. Peristome pentag- 

 onal in outline and transversely elongate ; a phyllode is faintly visible. 

 Periproct situated a short distance above the ambitus on the sloping 

 posterior abactinal surface, and beneath an overhanging rostrum of 

 the interambulacrum. Inferior surface covered with relatively large 

 scrobiculate tubercles. 



Belated forms. — This species differs from Cassidulus {Rhynchopij- 

 gus) califoriiicus (Anderson) in having a less rounded and tliinner 

 margin ; in that the test is relatively less elevated and has a sloping 

 posterior abactinal surface; in that the petals of the trivium are rela- 



