PLATE 41. 



Lovenechinus missouriensis (Jackson). Page 337. 



Fig. 1. Same specimen as photographs, Plate 39, figs. 4 and 5. X 0.7. In the ambulacra, the plates ventrally are all 

 primaries, at the mid-zone demi- and occluded, near the ocular all primaries. The bases of the interambulacra are 

 in part restored as indicated by dotted lines. In area A, the third plate, P, of column 3 is by exception a pentagon, 

 and its wanting side is compensated for by an adjacent heptagonal plate, H; the initial plate of column 5 is in the 

 eighth row, next it is an exceptional pentagon, P. In the ninth row there are only four plates, but an octagonal 

 plate, O, compensates for the sides wanting in the two adjacent pentagons, 5 and P. In area C, column 5 originates 

 to the left of the center, an exception; a peculiar pentagonal plate, P, in column 4 is compensated for by an adjacent 

 heptagonal plate, H. In area E, a sixth column is represented by a single plate 6, associated with which are a pentag- 

 onal plate, P, and two heptagonal plates, H, in column 5. A similar condition exists in area I. In area G, the sixth 

 column is represented by two plates, 6, 6, with an associated pentagonal plate, P, and two heptagonal plates, H. In 

 this specimen there are 26 plates in an adradial column, whereas in the young specimen, Plate 39, fig. 1 ; Plate 40, 

 fig. 1, there are but 13 or 14 plates in an adradial column. This larger specimen is about three times as large as the 

 smaller specimen yet there are only about twice as many plates in an adradial column. Here as I previously showed 

 (Jackson, 1899, p. 130) in Strongylocentrotus and Arbacia the increase of size in growth of the individual is attained 

 proportionately more by an increase in the size of the plates than it is by the increase in the number of rows of plates 

 (p. 342). 



Fig. 2. Same specimen as photograph, Plate 39, figs. 1, 2, also Plate 40, figs. 1, 2. Young individual. X 4.3. Ambul- 

 acral plates are all primaries dorsally. Interambulacra abut against the oculars laterally. Oculars D and F are 

 exsert, but all others apparently reach the periproct (p. 89) ; an ocular pore is in each plate in this internal view, but 

 whether the pores reached the surface is doubtful; probably they did not (p. 89). Genitals A, C, and G have 

 three pores each; the pores of the other genitals are doubtful (p. 341). 



Fig. 3. Same specimen as photograph, Plate 39, fig. 3. X 2.1. Column 5 drops out dorsally in areas A to E, but reaches 

 the apical disc in areas G and I. Oculars are all insert; genitals have four or five pores each, an unusually large 

 number for the species (p. 342). 



