ON A NEW GENUS AND SPECIES OF BLASTOIDS. 



83 



face of the body. They rest with their lateral sides against the inflected 

 upper part of the limbs, and form more or less strongly marked edges 

 or elevated angular ridges, which extend out interradially from near 

 the oral opening to the end of the plates. The hydrospires are placed 

 to both sides of the so-called "oral ridges," and are all located within 

 the Umits of the interradials, only small portions of them being con- 

 tinued along the sides of the limbs. In the more clav'ate form with 

 small interradials, for which I have proposed the generic name Hetero- 

 sc/iisma, the "orals" are only partly exposed to view, the visible ])art 

 occupying a small space around the mouth, the concealed portions, 

 which give origin to the two inner hydrosiiires, being overlapped by 

 the ends of two contiguous limbs. There is in Hetcroschisina, in the 

 proper sense of the word, exteriorly no "oi^al ridge," as the edge is here 

 formed by the limbs. The limbs are extended interradially into high 

 l^yramids with steep sides, of which two of the walls form the sides of 

 the radial sinus. The hydrospires are located, with the exception of 

 the two inner ones, within the pyramids, being exposed along the sides 

 of the sinus, nowhere connecting externally with the interradial plates. 

 In Cadaster the hydrospires enter the body nearly at right-angles, and 

 the walls are placed almost parallel to each other. In Heteroschisma 

 the hydrospires stand obliquely to the sides of the sinus, and they are 

 arranged closely around the mouth, while those of Cadaster are placed 

 away from the mouth. The differences between the two genera and 

 the allied Phcenoschisma are shown in the accompanying table : 



Heteroschisma includes the following species: Heteraschisma gra- 

 cile, the type of the genus; Heteroschisma alternatum, and H. altenia- 

 tinii, var. elongatum, Wachsmuth,-' all from the lower part of the Ham- 

 ilton group, Devonian. 



* Dr. Knapp, of Louisville, Kentucky, had the kindness to send me, for examination and 

 study, his large collection of Louisville Codasters, consisting- of nearly forty specimens, in all 

 stages of growth, and embracing at least two well marked species. Lyon, in describing his 



