108 B. ETHEKIDGE, JUN., ON ASTROCRINITES. 



The small spaces separating the inner contiguous sockets (c and d, 

 fig. 17) are prominent, and give a longitudinal ridge-like appearance 

 to both sides of the pseudambulacrum, better seen in the cross sec- 

 tion (e, fig. 18). The slit-like opening (e, fig. 17) may represent the 

 pore of the pore-plate in a Pentremite, when the smaller plate (Ji, 

 fig. 17) would perhaps be identical with the supplementary pore- 

 plate in the same genus ; it appears, however, in the present organ- 

 ism to be itself sometimes pierced by a pore. On the underside 

 of the pseudambulacrum, at the base or the end near the ventral 

 aperture, is a peculiar projecting process (e, fig. 19). 



(d) Apertures. — The ventral central aperture, when the spear- 

 head-shaped plates («, fig. 5) are in position, is in the form of a 

 St. George's cross; but when these are removed it is seen as in 

 fig. 4, much larger and quadrangular. The crushed condition and 

 delicate nature of this part of the calyx in all these little fossils 

 render it extremely difficult to form an absolutely correct idea as 

 to what was the perfect state of the central aperture. I have not 

 seen any evidence of supplementary pores surrounding the latter 

 with which the pseudambulacral grooves communicate, similar to 

 those discovered by Mr. Billings in the apex of Pentremites conoideus, 

 Hall*. 



The excentric aperture (fig. 5, & a, fig. 20) is pyriform and filled 

 in, or perhaps covered by a plate very valve- or lid-like in cha- 

 racter. It is a narrow elongate plate (h, fig. 5 ; g, fig. 20), slightly 

 broader at the middle portion than at each extremity, the outer of 

 which is split up into a series of small prolongations or fingers, 

 resting on the margins of the aperture. In the figured specimen 

 (fig. 5) the two terminal ones are the longest, whilst on the best- 

 preserved side of the plate there are three lateral digitations ; the 

 former, or two terminal ones, rest one on each side of the previously 

 mentioned ridge, running inwards towards a small cup -like depression 

 for, fig. 5; 6, fig. 14). 



(e) Ornamentation. — The dorsal surface and interradial lobes are 

 ornamented with tubercles — those of the dorsal surface sharp and 

 tooth-like (a, fig. 24), those of the plates short, conical, bluntly 

 pointed, and impunctatc, fluted down the sides, all set independently 

 of one another, and with a plain smooth apex (figs. 21 & 22). The 

 convex-crested plates on the ventral surface have usually each three 

 or more rows of these tubercles well developed, the central row 

 being the largest. 



(f ) Spines. — Adhering to one of the specimens by some particles 

 of matrix, but not attached in place, is a microscopic spine (fig. 23). 



(g) Madreporiform Tubercle. — I have quite failed to detect any 

 body or projection of or on the surface which could for one moment 

 be construed as representing this organ. It is true that on one of 

 the specimens (c, fig. 3; b, fig. 24) obtained by Mr. Bennie at 

 Carlops, there is a peculiar body, which I at first thought might 

 be the "eminence on the dorsal surface" mentioned by Messrs. 

 Austin in A. tetragonus, but was puzzled how to account for its pre- 



* Pal. Fossils (Geol. Sury. Canada), ii. pt. 1, p. 103. 



