ON A NEW GENUS AND SPECIES OF BLASTOIDS. 85 



approaching the basi-radial suture. Intermediate between the am- 

 bulacra there are five pyramids, formed by the junction of the adjacent 

 Hmbs of two contiguous radials,' without the assistance of interradial 

 plates. Four of them are sharply pointed, projecting conspicuously 

 above the level of the summit; the fifth, the one containing the anal 

 orifice, is a little lower and truncate. Ambulacra placed at the 

 bottom of a deep sinus, curving gently in an upward direction. 

 Greatest width of the body across the lips, where the section is 

 strictly pentagonal, while it is obscurely triangular across the basals. 

 Average length and width, as taken from eleven specimens, as eight to 

 to five; actual length, from three to six tenths of an inch. Surface of 

 the plates perfectly smooth, without ornamentation. 



Basals long, in form of an elongate cup ; column-like, extended at 

 the lower end; upper face somewhat excavated for the reception of 

 the radials, with an obtuse angle beneath their juncture. 



Radials moderately increasing in width to the sinus. The length of 

 the radial body equal to, or. surpassing, its greatest length, and eijual to 

 the length of the basals. The limbs occupy less than one-third the en- 

 tire length of the plate ; they are slightly bent inward, those of two con- 

 tiguous radials forming a triangle, of which the horizontal side (between 

 the lips of the adjoining radials) is but little longer than the two lateral 

 sides. At the a/.ygous interradius the upper angle is truncated by the 

 anal aperture, and the outer side of the pyramid is more slojiing. Sinus 

 short, and remarkably deep. 



The interradial plates are small, and only partly exposed to view, 

 one-half or more of each one being hidden beneath the radials. The 

 exposed part, which consists of barely more than what might be called 

 the lips of the mouth, is slightly projecting along the margin ; it is in 

 form rhomboidal, but the angle toward the radials is covered by the 

 tips of the overlapping limbs. The concealed portions are longer than 

 wide, and their distal end is somewhat extended outward and down- 

 ward. The description of the interradial plates was made from a speci- 

 men in which the greater part of the limbs had weathered away, thereby 

 exposing the parts underneath. As seen in this specimen, the lateral 

 sides give off the two inner hydrospires in each group, but not the 

 others. The interradial ])late of the azygous side is constructed some- 

 what different. The parts which are covered by the limbs, and form 

 the ridges, take here a more inward direction, and compose the sides 

 and inner floor of a little cavity, which forms the entrance to the anal 

 aperture. The opening into this cavity is large, somewhat broadly sub- 



