CLARK: NEW BLASTOIDS AND BRACHIOPODS. 365 



Pextremites divergens, sp. nov. 



Plate 1, fig. 7-10. 



Description. — Small, thickest at the base of the ambulacra. Width 

 and height subequal, the body being slightly higher than wide. Basal 

 portion obconical, occupying about one third the length of the speci- 

 men. The basal plates are obscured in the type. The radials are 

 prominently angular below the ambulacra, forming a longitudinal 

 ridge extending from the base of the ambulacra to the basals; the 

 spaces between these ridges are concave. The interambulacral areas 

 narrow rapidly upwards and are depressed along each median suture; 

 there is no rim bordering the interambulacral areas. The deltoids 

 are small, less than a quarter the length of the whole body, acuminate, 

 the tip somewhat incurved towards the oral aperture. Oral opening 

 and spiracles large, shape uncertain. The ambulacra] areas enlarge 

 rapidly upwards, the lower end distinctly rounded in outline, and 

 not angular. There are from fifteen to sixteen side-plates in the 

 space of five millimeters. 



Dimensions of two specimens in millimeters. 



Height 11. — 



Maximum diameter 10 . 8.5 



Length of ambulacral area 7.5 6 . 25 



Maximum width of ambulacral plates 3 . 25 3 . 



Length of deltoid plates 2.5 1.5 



Maximum width of deltoid plates 1.0 .5 



Average number of side-plates in 5 mm 16. 15-16 



Dimensions of the tioo specimens adjusted to a maximum diameter of 



18 mm. 



Height 20. — 



Maximum diameter 18 . 18 . 



Length of ambulacral area 13.6 13.2 



Maximum width of ambulacral plates 5.9 6.3 



Length of deltoid plates 4.5 3.1 



Maximum width of deltoid plates 1.8 1.1 



Formation and locality. — The specimens were collected by the author 

 from the limestone member of the Quadrant formation at Old Baldy. 



