CLARK: NEW BLASTOIDS AND BRACHIOPODS. 365 



Pentremites 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 ambulacral 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. 



Dimensioiis 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 two 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. 



