May, 1909. 



New Echinoids — Slocom. 



11 



The dimensions of a number of practical^ perfect specimens are 

 as follows: 



H. lacunosus resembles H. parastatus in general form and pro- 

 portions, but is distinguished from that species by its smaller size 

 and by the sunken areoles of the tubercles. Moreover, the posterior 

 interambulacral area is rounded, while in H. parastatus it is in the 

 form of a ridge. H. lacunosus is similar to H. Stella in size, but differs 

 from it in the shape of the fasciole, the sunken areoles and the form 

 of the anterior margin. It resembles H. dalli in having sunken areoles, 

 but in general form these two species are quite dissimilar. The 

 specific name adopted refers to the sunken areoles by which the species 

 is distinguished. 



Locality: This species is abundant at all three of the outcrops 

 visited at Pontotoc and about 150 specimens were collected. The 

 test is very thin and and fragile, so that of the 150 specimens less 

 than a dozen were unbroken. Three specimens which undoubtedly 

 belong to this species were also collected by the writer at Houston, 

 Mississippi, associated with fossils of the Selma Chalk, but as the Rip- 

 ley and Selma formations are both reported from Houston and the 

 fossils were found at the bottom of gullies of some size, it is quite 

 probable that the echinoids were of Ripley age. , 



Genus LINTHIA Merian 1853. 



Test variable in size, oval or cordiform, grooved anteriorly, 

 subacuminate or truncated posteriorly, tumid and gibbous dorsally, 

 almost flat ventrally. Apical system small, eccentric anteriorly, 

 composed of four perforated genital plates, one of which forms the 

 madreporite, and five small radial plates. Ambulacral areas diverse; 

 anterior one in a broad groove, pores round and small. Antero- 

 lateral pair with petaloid parts in grooves, moderately long, diver- 

 gent, nearly closing distally; pairs of pores equal or subequal. Pos- 

 tero-lateral pair also in sunken grooves, less divergent and shorter 



