LEPIDESTHES. 



431 



the one most essential feature in their morphology and evolution, and in its great proportionate 

 development to the rest of the test, this species takes rank among the most specialized of known 

 types (p. 234). 



The ambulacra, as far aborally as known, have 16 columns of plates in each area, and, as 

 stated, are several times the width of the interambulacra instead of about twice the width, as 

 in Lepidesthes colletti. As the impressions of the plates are internal molds, the details are not 

 the same as they would be on the exterior, but the plates are wide and would evidently be 

 hexagonal if the external sutures were visible. The pore-pairs are situated about in the middle 

 line in the lower or adoral half of each plate, a general character of the interior in this genus 

 (compare p. 418, Plate 67, figs. 15, 16). The ambulacral plates evidently imbricate strongly 

 ventrally and laterally bevel under the adradials. 



The interambulacral areas, as far as preserved, have four columns of plates in an area 

 (Plate 71, fig. 2), and the same is true of the dorsal side (text-fig. 252), as seen, not very clearly, 

 in Plate 72, fig. 2. As there are four columns, both ventrally and dorsally, this is doubtless the 

 character of the area for the parts which are missing, 

 except the ventral developing area near the peristome. 

 The interambulacral plates are all small, about equal 

 in height to the ambulacrals, both ventrally and dor- 

 sally. They imbricate strongly aborally and from the 

 center laterally and over the ambulacra on the adradial 

 sutures. On the exterior, as shown by external molds, 

 the plates are rounded in outline as usual, and bear 

 small secondary tubercles (Plate 73, fig. 1). Crowded 

 masses of spines occur on both specimens as external 

 molds. They are all slender, filiform, swollen at the 

 base, and about 3 to 4 mm. long (Plate 73, fig. 2). 

 Peristomal, apical, and periproctal plates are unknown 

 in this species, but ventrally there are impressions of a 

 powerful lantern. 



This species has the same number of columns of 

 ambulacral and interambulacral plates as Lepidesthes 



colletti, but in the extreme width of the ambulacra and narrowness of the interambulacra, it 

 may well be considered the most specialized species of the genus. It is also geologically the 

 highest species of the genus, as it comes from the Coal Measures or Carboniferous proper, 

 whereas all other species are found in the Devonian or Lower Carboniferous. 



Putnam Hill Limestone, Carboniferous (Coal Measures), New Lexington, Perry County, 

 Ohio, in the collection of Mr. Eber Hyde, holotype no. 524, paratype no. 525. 



Text-fig. 252. — Lepidesthes extremis sp. nov. 

 Internal mold of the dorsal side, same specimen 

 as Plate 72, fig. 2. Holotype. X about 1.8. 



