LEPIDECHINUS. 399 



In the holotype, which is in the Museum of Comparative Zoology, the dorsal half of the 

 test is preserved (Plate 62, fig. 2; Plate 63, figs. 5, 6). In areas A, E, and I the sixth column 

 drops out passing dorsally and terminates in a pentagonal plate, an apex of which points dor- 

 sally; and in areas C and G the fifth column drops out similarly. In area E the fifth column 

 also drops out, but two rows later than column 6. The terminal pentagons in several cases have 

 a heptagonal plate on their dorsal border. These might easily be taken for the point of intro- 

 duction of columns, bat this is the dorsal, not the ventral portion of the test, as shown by the 

 direction of imbrication of plates. This specimen has very clear ambulacral detail which is 

 taken to represent the species character. 



In Mr. Springer's specimen (Plate 62, fig. 4; Plate 63, figs. 9-11) the plates are worn, 

 but the imbrication is clear, as shown in Plate 63, figs. 10 and 11. Ventrally there are five 

 columns, the sixth coming in below the mid-zone. The ambulacral plates ventrally are all 

 typical primaries with pore-pairs uniserial, but at the mid-zone in this specimen there is a tend- 

 ency for alternate plates to be expanded on the lateral border and the plates between narrowed. 

 There is nothing of this seen in the type, but otherwise the specimen has the characters of 

 this species. 



The Museum of Comparative Zoology specimen, which is seen from the interior, is very 

 interesting (Plate 62, fig. 3; Plate 63, figs. 7, 8). There are three interambulacral and four 

 ambulacral areas. The interambulacral columns in each area are all continued nearly or 

 quite to the apical disc instead of dropping out dorsally, as in Plate 63, fig. 5. The ambulacral 

 plates and apical disc of this choice specimen are considered above. 



*Lepidechinus imbricatus Hall. 



Plate 62, fig. 5; Plate 64, fig. 1. 



Lepidechinus imbricatus Hall, 1861, p. IS; 1868, p. 296; Loveii, 1874, p. 44; Keyes, 1895, p. 192; Jackson, 

 1896, pp.226, 242; non A. Agassiz, 1904, p. SO; Klem, 1904, p. 21; Lambert and Thiery, 1910, p. 122. 

 Lepidocentrus imbricatus Meek, 1874, p. 375. 

 Lepidechinus intricatus Pomel, 18S3, p. 113. 



In the type specimen, which is in the Museum of Comparative Zoology, the test is sphe- 

 roidal. The ambulacra at the mid-zone measure about 3 mm., and the interambulacra about 

 20 mm. in width. 



The ambulacra are narrow, composed throughout each area of two columns of low pri- 

 mary plates which imbricate strongly adorally and bevel under the adjacent adambulacrals. 

 Pore-pairs are uniserial, situated near the outer border of each plate. Two and a half 

 ambulacral plates equal the height of an adambulacral. The interambulacra are broad, with, 

 at the mid-zone, eight columns of plates, which are small, curving outward, and rounded 

 on the suture lines. They imbricate strongly aborally and from the center laterally and 



