318 ROBERT TRACY JACKSON ON ECHINI. 



In the type there are six or seven columns of plates in an interambulacral area at the 

 mid-zone. In area A there are six columns, and below the mid-zone the introduction of 

 the fifth and sixth columns is seen, both originating as usual with a pentagonal plate. By this 

 means the specimen was oriented, and it will be noticed that the orientation of my figure is 

 the reverse of that given by M'Coy. In this area. A, the six columns extend dorsally to the 

 covering matrix. In interambulacrum C there are seven columns at the mid-zone. The 

 seventh column consists of four plates only, on one of which the letter C occurs in Plate 32, fig. 5. 

 Ventrally and dorsally to the seventh there are six columns in this area. Areas E and G are 

 imperfect, for the most part internal molds, and the full nunil^er of columns was not ascertained. 

 Interambulacrum I is also an internal mold, but the impress of six columns of plates was clearly 

 ascertained at the mid-zone. In one of the British Museum specimens (E 3,652) there are seven 

 columns of plates in the only .interambulacral area clearly preserved. Of two other British 

 Museum specimens (E 361) on a single slab, one has five columns of plates in all five inter- 

 ambulacral areas (Plate 32, fig. 4), whereas the other has five columns in one area, but six in two 

 other areas. 



On account of the matrix covering the dorsal area, the features of this part are unknown 

 in the type. In the British Museum specimen (Plate 34, fig. 6), the apical disc is small, the 

 oculars are all insert, genitals wide, low (pores not visible), and the periproct has numerous 

 small angular plates as usual in the Palaeozoic. 



M'Coy's type is in Trinity College Museum, Dublin, where I studied it through the kind- 

 ness of Professor Joly. There is no locality given, but it bears the label, "Presented by Dr. 

 A. N. Fox, Staff Assistant Surgeon, 1 Nov., 1867." For several years earlier it had been in 

 the possession of the Rev. S. W. Fox. According to Baily (1865c, p. 89) the, specimen was 

 supposed to have come from the limestone of the County Kildare, but that was not certain. 

 A plaster cast of this valuable specimen is in the Museum of Practical Geology in London, 

 and another in the Museum of Comparative Zoology. 



Confusion has been introduced as to the structure of this species by de Koninck's (1870) 

 description of a specimen which he referred to Palaechinus sphaericus M'Coy. Through the 

 great kindness of my friend Dr. F. A. Bather, the specimen was borrowed from the York Museum, 

 and it proves that the description was incorrect in several particulars. The specimen is not 

 a Maccoya sphaerica, and does not even belong to the genus Maccoya, having a very different 

 ambulacral structure. It is here referred to Lovenechinus lacazei (text-figs. 240-243, p. 331; 

 Plate 35, fig. 7). From this it occurs that statements in regard to the absence of oculars 

 (entirely wrong), structure of the genital plates (also incorrect), and the number of inter- 

 ambulacral columns ascribed to sphaerica, as far as based on de Koninck's observations, are 

 erroneous (footnote, p. 303). 



Lower Carboniferous, probably County Kildare, Ireland; on the authority of Baily 



