LOVENECHINUS. 347 



by the right half-area only. The left half of ambulacrum B and the right portion of inter- 

 ambulacrum C have been pushed under areas A, B so as to be quite hidden from view. Inter- 

 ambulacrum C is represented by the left adradial and one adjacent median column of hex- 

 agonal plates. Of ambulacrum D, the whole width of the area is in place, though not very 

 clearly seen. Interambulacrum E has six columns of plates, as can be seen dorsally, although 

 they are somewhat displaced. 



A complete test is unknown ; but the shape as preserved indicates that the entire specimen 

 was probably spheroidal, and the size of the plates shows that the whole specimen must have 

 been very large, one of the largest of known Palaeozoic Echini. The height of the specimen as 

 it exists is 115 mm., and the width 150 mm. The half ambulacrum B measures 7.5 mm. in 

 width, therefore the whole area would measure 15 mm. in width. Interambulacrum A measures 

 55 mm. in width. Adding one adambulacral column on the right (as this at least is wanting), 

 the width on the basis of six columns would be about 65 mm. Assuming 15 mm. for the width 

 of the ambulacrum, and 65 mm. for the interambulacrum, the circumference would be about 

 400 mm. and the diameter about 127 mm. The interambulacral plates are very large, the 

 pentagonal adradials measuring up to 11 mm. in width by 8 nmi. in height, and the largest 

 hexagonals 12 to 13 mm. in width by 8 mm. in height. With this great areal size they are 

 relatively very thin, about 2 mm. in thickness. 



The ambidacra are relatively narrow, with four columns of plates throughout most of the 

 area, there being two columns of wider occluded and two of narrower demi-plates in each half- 

 area (Plate 47, figs. 3, 5) The outer ends of the occluded plates fit between the inner tongue- 

 like extensions of the demi-plates as in Lovenechinus missouriensis. The pore-pairs are in well 

 marked peripodia and are biserial in arrangement, each pair situated in the outer ends of the 

 occluded and demi-plates as usual in the genus. About four demi-plates equal the height of 

 an adradial. The extreme ventral part of the test is unknown, but as far ventrally as preserved 

 in area D (Plate 47, fig. 4) all ambulacral plates meet the middle of the half-area, but alternate 

 plates are primaries expanded marginally, and occluded or cut off from interambulacral contact 

 by enlargement of their fellows. This character is like that typical of adult Maccoya (Plate 

 33, fig. 7), and also like that seen as a second stage in development in Lovenechinus ynissou- 

 riensis (Plate 42, fig. 1). On the reverse side of the specimen are several excellent fragments 

 of ambulacra seen from the interior of the test. In these the demi- and occluded plates are of 

 about equal width, and the pore-pairs lie near the middle of the half-areas, as seen in the in- 

 ternal view of Lovenechinus missouriensis (Plate 43, fig. 4). 



The interambulacra are very wide, composed of probably six columns in each area. In 

 area A (Plate 47, fig. 3) the left adambulacral column of pentagonal plates is in place, and also 

 four columns of hexagonal plates. I have indicated by dotted lines a right adambulacral 

 column which probably would complete the area. Six columns can be made out dorsally in 



