14 



Trans. Acad. Sci. of St. Louis. 



integument does not run close to the margin of the sinus in 

 the vicinity of the ovarian or genital openings, making 

 them appear as little slits instead of round openings. It runs 

 in the shape of a letter j\ inverted with the two arms extend- 

 ing out and downward to the apex of the ambulacrum. Each 

 arm covers one-half of the ambulacral 

 surface, forming w^ith the opposite one 

 a longitudinal groove in the center (the 

 so-called foot groove ) . This foot groove 

 and the little transverse grooves at 

 each side of it are covered with little 

 scales, so that, in specimens very well 

 preserved, the ambulacrum does not 

 ^'^- ^' show any transversely striated surface at 



all, but appears rather smooth or granulated with a little crest 

 in the center. The whole covering is of a uniform character, 

 except on the summit, where the scales surrounding the ova- 

 rian or genital apertures (at least in the typical species) are 

 fully ten times as long and placed erect on the underlying 

 membrane, — see Fig. 5 and Plate II., Fig. 2, 3, 5, — forming 

 in this way a part of the cone-shaped body which has been 

 observed on the summit of many species. Their physiologi- 

 cal function is still unknown, but probably it was to protect 

 the finer inner ovarian tubes. Besides the scales we find 

 on the posterior side above the anal opening, on very 

 well preserved specimens, a small proboscis about one 

 fourth of an inch in length, constructed of small hexago- 

 nal pieces, as shown in Fig. 6 and 7. To my knowledge 

 it is the first time that such a body has been observed on a 

 Blastoid. I found this appendix on Pentremites conoideus 



and have now four speci- 

 mens of it showing this, 

 so far unknown, organ. 

 All four specimens are in 

 an excellent state of pres- 

 ervation and show also 

 the pinnulae preserved. 

 I am inclined to believe 

 ^' that similar organs existed 



hiG. 



