58 CATALOGUE OF THE BLASTOIDEA. 



This seems to have led Hambach ' to describe the whole ambulacrum as covered by a 

 zigzag plicated integument which " was probably of an elastic texture during the 

 lifetime of the animal. It commences at the apex of the ambulacral field, running 

 in a zigzag from the lateral margin to the median line, so that the poral openings are 

 always placed between two returning folds, which are flattened here to form a sort of 

 articulating surface for the pinnulse. It ascends in this manner, covering half of the 

 ambulacral field to the summit of the calyx, where it surrounds in a very acute angle 

 two of the ovarian openings, and descends in a like manner on the following ambu- 

 lacral field." The last portion of this description and the figures which illustrate it, 

 too-ether with others published later, show that Hambach is here referring to the 

 crenulation on the central ends of the deltoid plates which border the peristome, as 

 shown in many of our figures of Pentremitidea, Mesoblastus, Granatocrinus, Schizo- 

 blastus, Cadaster, &c. (PL IV. figs. 1, 8; PL VII. figs. 11, 13, 14, 15; PL VIII. 

 figs. 2, 4, 9 ; PL IX. figs. 8, 14 ; PL XII. fig. 4 ; PL XIII. fig. 14). It is often 

 more or less invisible in weathered specimens (PL I. figs. 4-6, 10, 11 ; PL III. 

 fig. 14; PL IV. figs. 14, 17 ; PL VI. figs. 7, 13 ; PL X.figs. 8, 10 ; PL XII. fig. 1) ; 

 while in Mesoblastus crenulatus the hollows have been sometimes worn away so much 

 as to look almost like a row of small pits on the central end of the deltoid (PL VI. 

 ficr. 8). It has been already explained how this crenulation is continued outwards 

 alon°' the edges of the median groove on the lancet-plate, whether the latter is com- 

 pletely exposed, as in Pentremites, or partially concealed by side plates (PL VII. 

 fig. 14; PL XIII. figs. 4, 14) ; and Hambach's description of the integument as 

 running in a zigzag from the lateral margin of the ambulacrum to the median line, 

 together with his figures illustrating it, can refer to nothing else than the crenulated 

 lateral branches of the food-groove, which are well shown in PL I. figs. 1, 2, 9. In 

 the true Pentremites the uncovered surface of the lancet-plate bears the inner ends of 

 these lateral grooves, the outer ends of which coincide with the sutures between 

 successive side plates, and have much less distinctly crenulated edges, except in forms 

 like P. sulcatus (PL I. fig. 9). But in Granatocrinus, Mesoblastus, and other types 

 which have the side plates resting upon the lancet-plate, the median groove of the 

 latter has no lateral branches. It is well crenulated, as are also the inner ends of 

 the side plates (PL IV. fig. 4 ; PI. VIII. fig. 15 ; PL IX. figs. 7, 16), while in some 

 species, such as Granatocrinus Norwoodi, more or less of the distal border is 

 also crenulated (PL X. fig. 11). In those species which have the lancet-plate 

 entirely concealed by the side plates both the inner and the distal edges of the latter 

 may be strongly crenulated, as in Pentremitidea (PL IV. fig. 15 ; PL X. figs. 1, 3) ; 

 or there may be no markings on the side plates at all, except just at their finner 

 ends, as in some species of Mesoblastus, Granatocrinus, and Schizoblastus (PL VIII. 

 figs. 5, 21). 



1 Trans. St. Louis Acad. Sci. 1880, vol. iv. part 1, p. 150, plate a. fig. 10. 



