46 Dr. F. A. Bather on Protoechinus, Austin. 



imbrication, and the retention of the primordial interambu- 

 lacral in the basicoronal row, place the specimen without 

 doubt in the Lepidesthidae. 



The number of ambulacral columns removes it from 

 Lepidechinus and Perischodomus, which have only 2 ; also 

 from Lepidesthes with its 8 columns, and from Meehechinus 

 with 20. Perischocidaris has 6 columns, a number which 

 might conceivably, though improbably, have been attained 

 by Protoechinus anceps ; but the structure of both ambu- 

 lacrals and interambuiacrals is quite different. Proter ocularis 

 has only 4 columns of ambulacrals, but, on the other hand, 

 it has " many more columns of interambulacral plates than 

 are known in other genera of this family," certainly very 

 many more than in Protoechinus and of quite different 

 character. 



Of described genera there remains only Pholidocidaris. 

 According to Dr. Jackson's Key this has 4 to 6 ambulacral 

 columns, 5 to 6 interambulacral columns ; plates strongly 

 imbricating ; adoral ambulacrals much larger than those of 

 the adapical region. In the account of the genus on p. 433 

 it is added that the interambuiacrals are large and scale-like. 

 All this agrees well with Austin's specimen, which, if not 

 actually a Pholidocidaris, is at any rate "near to" it, as 

 Dr. Jackson himself {in litt.) concluded on the evidence of 

 a cast which I sent to him. 



It is, however, not clear why Dr. Jackson assigns a 

 possible four columns to the ambulacral area of Pholido- 

 cidaris, considering that in P. gaudriji and P. irregularis 

 there are six columns; it is only in the dorsal (adapical) 

 region of an immature individual of the latter species that 

 four columns are noted, and there may have been more at 

 the ambitus. The ambulacral areas are unknown in P. tenuis 

 and P. acuaria (YVhidborne, sub Protocidaris). Eveu if all 

 other species of Pholidocidaris had six columns to the area, 

 while Protoechinus anceps had only four, this would not of 

 itself be enough for generic distinction.* 



Apart from this, P. anceps differs from P. irregular is Meek 

 & "Wortken in the regular succession of its interambulacral 

 columns (though the irregularity observed in a specimen of 

 the latter species may be individual only), and in the appa- 

 rent differences of size between the various interambulacral 

 plates, those in the adoral region of P. irregularis being " of 

 about the same size" (Jackson). In P. irregularis the pore- 

 pairs of the adoral region are " about in the middle of each 

 plate"; vague though this statement is, I scarcely think 

 that Dr. Jackson would have applied it to P. anceps. 



From Pholidocidaris tenuis Tomquist, known only from 



