KEW FEATURES m PELAlSTECHHSTtTS CORALLINTTS. 713 



among the Glyphostomata, and this genus Pelanechinus resembles in 

 the shape and character of the aboral interambulacral plates. 



It seems to have affinities with both members of the Glyphostomata. 

 It resembles the Diadematidae in the possession of simply grooved 

 teeth, and the Echinidae in the structure of the ambulacral plates and 

 in the shape of the pedicellaria-stems. 



It thus occupies an intermediate position between the Echino- 

 thuridae and the Glyphostomata : and its peculiarities seem to entitle 

 it, if not to a separate position between the two families, at least to the 

 rank of a subfamily (which might be termed Pelanechinidae) among 

 the Glyphostomata, to which it seems most nearly allied. I may 

 say that this is the position assigned some weeks ago to Pelanechinus 

 by Prof. Alex. Agassiz from a cursory examination of my specimen. 

 He expressed an opinion that Pelanechinus was allied to the 

 Echinothuridae on the one hand and the Diadematidae on the other, 

 the affmitv being rather with the Diadematidae. 



Characters of Pelanechinus corallinus. 



Test. Circular, depressed, thin, and probably flexible. 



Interambulacral Areas. Narrow at the peristome, broadening 

 rapidly to more than twice the width of the ambulacra at the equator, 

 where there are eight rows of tubercles. 



Plates differ on the under and upper sides of the test ; on the 

 under surface elongated and with several tubercles ; on the upper 

 surface broader and with undulating boundaries, movable and pro- 

 bably overlapping from below upwards. One primary tubercle on 

 each plate. 



Ambulacral Areas. Less than half the width of the interambu- 

 lacra at the equator, narrowing gradually towards the peristome. 



Plates towards the apex of the oligoporous Echinoid type, with one 

 adoral primary and two aboral demiplates ; but at the equator 

 compounded into polyporous plates with nine pairs of pores arranged 

 in three oblique rows, one primary tubercle for each median primary. 



Peristome. Large, about 5 of the diameter of the test. Peri- 

 stomial notches of moderate depth. Peristomial membrane covered 

 with 10 rows of overlapping and imbricating calcified plates with 3 

 rows of tubercles on their free edges. Each plate with perforated 

 tubercles, spines, granules, and a pair of pores ; the successive pairs 

 forming a linear series continuous with the pores of the ambulacra. 



Dental Apparatus. Alveoli powerful. Teeth simply grooved. 



Apical System. Probably large and pentagonal. 



Primary Tubercles. Rather small, perforated, and mounted upon 

 elevated bases, with smooth and uncrenulated summits ; they are 

 uniform over both areas. 



Spines. Small, hollow, longitudinally striated. 



Pedicellarire. Three kinds (PL XXVIII.) :— 



(a) Small tridactyle from round the peristome, probably long- 

 stalked (fig. 1). 



a J. G. S. Xo. 172. 3 c 



