14 Field Museum of Natural History — Geology, Vol. IV. 



dividual variations. Owing to this tendency to variation, the spe- 

 -cific name variabilis has been adopted. 



Only one other species of this genus, L. tumidulus, has hitherto 

 been described from the American Cretaceous and that species is so 

 unlike L. variabilis that a detailed comparison is unnecessary. 



Locality: This species is from the Ripley Group and is quite 

 abundant both on the bluffs at One Mile Run and near the southern 

 •edge of the village at Pontotoc, Mississippi. Two casts which evi- 

 dently belong to this species were also collected by the writer in the 

 Owl Creek marls in Tippah County, Mississippi. 



A careful examination of the literature reveals the fact that com- 

 paratively little attention has hitherto been paid to the echinoids 

 of the Ripley Group of Mississippi. The following are all the references 

 that have been found by the writer: 



Journal of the Academy of Natural Sciences Philadelphia, 2d 

 series, Vol. 4, p. 291. i860. T. A. Conrad describes Cassidulus 

 ■abruptus and C. subquadratus both from Tippah County, Mississippi. 



Report of the Geology and Agriculture of the State of Mississippi, 

 i860, p. 92. E. W. Hilgard, State Geologist, gives a list of fossils 

 'collected from the strata of the Ripley Group in Tippah, Pontotoc 

 and Chickasaw Counties, in which the following echinoids are 

 listed : 



Hemiaster, 2 species. 



Cassidulus subquadratus Conrad. 



Cassidulus? (Echinanthus?) sp. 



Cassidulus shape of Faujasia apicalis. 



The Echinodermata of the United States, W. B. Clark, Bull. 

 U. S. G. S. Vol. 97, 1893. The following echinoids are noted from 

 the Ripley Group: 



Botriopygus alabamensis Clark Alabama. 



Cassidulus cequoreus Morton Alabama. 



Cassidulus micrococcus Gabb Eufaula, Alabama. 



Cassidulus porrectus Clark Eufaula, Alabama. 



Cassidulus subconicus Clark Mississippi. 



Cassidulus subquadratus Conrad Holly Springs, Mississippi. 



Hemiaster parastatus Morton Alabama. 



Cassidulus abruptus Conrad is mentioned as a doubtful species. 



Geology and Mineral Resources of Mississippi, A. F. Crider. Bull. 

 U. S. G. S. Vol. 283, 1906, p. 20. A list of the Ripley fauna at Owl 

 Creek, Tippah County, Mississippi, as collected by Dr. T. W. Stanton 

 is given in which Cassidulus subconicus and C. subquadratus are 

 mentioned. 



