PHOLIDECHINUS. 301 



In the holotype (Plate 27, fig. 1; Plate 28, figs. 2, 3, 9) there are nine columns of inter- 

 ambulacral plates in each area at the mid-zone, but a tenth appears dorsally in area C. The 

 beveling of plates is seen below the initial plate of column 8, some spines are in place, and the 

 delicate flanges described as bordering the plates are well preserved. 



In Mr. Braun's specimen (Plate 27, fig. 2; Plate 28, fig. 1) there are nine columns of plates 

 at the mid-zone in each interambulacral area. The primordial interambulacral plates are in 

 place in the basicoronal row, two plates in the second, three in the third, and four in the fourth 

 row, above which additional columns come in with a moderate, not an accelerated rate of 

 development. Low, wide ambulacral plates cover the peristomal area, and the teeth are 

 in place. The British Museum specimen (Plate 27, fig. 3; Plate 28, figs. 4-6) has ten columns 

 of plates in each interambulacral area, in both originating at or below the mid-zone; ambula- 

 cral detail at the mid-zone is clear. 



In Yale University Museum there are two lanterns in the D. A. Barrett Collection from 

 Crawfordsville belonging to this species, which are remarkably perfect in preservation, being 

 the best specimens of this structure so far known in any Palaeozoic echinoid. One of these 

 specimens I mentioned in my earlier paper (1896, p. 213), but they have not been described. 

 The two are essentially similar except that one is laterally compressed. The more perfect speci- 

 men is shown in Plate 27, figs. 4-6, and in its relations to the lanterns of other representative 

 Echini in text-fig. 207, p. 184. It is important in itself, also because it is typical of all lanterns 

 known from the Palaeozoic formations, others known differing from it only in trifling details. 

 In side view with teeth in place (Plate 27, fig. 6) it is inclined at a very wide angle of about 90 

 degrees, the width of the top being very nearly twice the total height from the tips of the teeth. 

 This wide angle, which I have described as inclined, is characteristic of all Palaeozoic lanterns, 

 also of the lanterns of young modern regular Echini. The teeth are grooved, meet in a point 

 ventrally, and dorsally extend to a point just above the base of the foramen magnum, so that 

 they are seen in side view. This is evidently the dorsal limit of the calcified portion of the tooth, 

 beyond which the uncalcified portion would doubtless extend in life as in Strongylocentrotus 

 (Plate 5, figs. 6, 9). The pyramids are very wide-angled, with a rather shallow foramen mag- 

 num. Hollows are on either side of the face view, in which the retractor muscles took origin; 

 the sides of the pyramids are curved, admitting of relatively long interpyramidal muscles. 

 The lateral wings of the pyramid are wide, as in Oligoporus (Plate 50, fig. 11), a resultant of 

 the inclined angle of the lantern. A narrow epiphysis caps each half-pyramid, seen in face 

 view (Plate 27, fig. 6), and in dorsal view (Plate 27, fig. 5), it extends inward, narrowing toward 

 the oesophageal cavity. A typical brace rests on and interlocks with the two adjacent epiphyses 

 as shown in ventral, side, and dorsal views. The brace has the usual condyles and other out- 

 lines of modern regular Echini. In one area, D, of figure 5, a compass exists, slightly displaced, 

 and apparently fragments of two other compasses in areas B and J. The compass is arched 



