Hambach — Revision of the Blastoideae. 15 



in all typical species. At the outer margin of the ambulac- 

 rum, where the outward running ribbon returns to the center 

 of the field, the ribbon is twisted over so that the fold facili- 

 tating the return is the under surface of the ribbon and 

 becomes the articulation surf ace of the pinnulae ; see Plate II., 

 Fig. 5. These pinnulae are little filaments of various lengths 

 extending in some species as much beyond the summit as the 

 entire length of the calyx, or even more. They consist of a 

 single row of calcareous particles, wedge-shaped in form and 

 about as broad as long. 



As evidence to support the foregoing assertion, ^. e., the 

 flexibilitv and organic nature of the ambulacral integument, 

 I give in Figures 1-7, Plate I., representations of some 

 pathologic specimens selected from a large amount of mate- 

 rial collected for this purpose. I have over fifty such patho- 

 logic specimens, showing various kinds of injuries and the 

 subsequent restoration of the injured parts, which would 

 have been impossible had the integument been inorganic mat- 

 ter only, as supposed by Carpenter. All specimens figured, 

 belong to the species Ptntremites sulcatus. Plate I., Fig. 6, 

 shows an injury near the middle of the ambulacrum; Fig. 5 

 a similar injury on one side of the field and on the other side 

 the loss of half the poral pieces and the subsequent restora- 

 tion of the integument. Fig. 1 and 2 show the flexion of 

 the transverse ridges into a sigmoid form and the partly 

 compressed shape of the genital openings ; Fig. 7 and Plate II., 

 Fig. 7 show the unevenness of the integument at the outer 

 margin near the sinus. 



The acute points at the beginning of the ambulacral in- 

 tegument are the only covering for the central orifice. (The 

 surrounding genital openings are entirely out of the ques- 

 tion.) The different descriptions and illustrations given 

 (which all differ from each other) are erroneous representa- 

 tions due to mistaking foreign matter for covering plates, as 

 already expressed in my first paper.* Nothing is more natural 

 than that some of the little scales or particles of broken 

 pinnulae should drop into some of the summit openings and 



Transactions of The St. Louis Academy of Science, Vol. IV., p. 150. 



