LOVENECHINUS. 349 



Collection, no. 8,115; also three additional incomplete specimens from the same locahty and 

 in the same collection. 



Although crushed, the type specimen is so completely preserved that I am able to repre- 

 sent it spread out by the Loven method (Plate 45, fig. 1), and it presents interesting develop- 

 mental characters in both ths ambulacra and the interambulacra. Ventrally, for a short 

 distance, ambulacral plates are primaries (Plate 45, fig. 2), above which follow primary and 

 demi-plates immediately, and these again are shortly followed by the typical occluded and demi- 

 plates characteristic of the type. No stage of primary and occluded plates (such as occurs in 

 Lovenechinus missouriensis, Plate 42, fig. 1) was found in this species, and it has apparently 

 been skipped by acceleration of development. This is interesting, for in other characters it 

 is the highest species in the genus, and it is in just such a case of highest species that accel- 

 eration is most marked, as shown by Hyatt. Dorsally, close to the oculars (Plate 45, fig. 4) 

 high, narrow primary plates exist as a localized primitive stage, but, passing adorally, they 

 quickly change into the characteristic four columns of demi- and occluded plates. 



The interambulacra with only slight reconstruction (indicated by dotted lines) are shown 

 throughout each area (Plate 45, figs. 1,2). Ventrally, in each area (excepting C and G, in which 

 they are restored) there are two plates in the basicoronal row and three plates in the second 

 row. In four areas the initial plate of column 3 is hexagonal as usual, with the initial pentagon 

 of column 4 in the next succeeding row. In area C, however, there are two rows of three plates 

 each before column 4 originates in the fourth row. As a result of this difference, the initial 

 plate of column 3 is pentagonal and the succeeding plate is heptagonal, having one side added 

 to compensate for the one side short in pentagon 4 (p. 68). A similar case of this rare varia- 

 tion of a later introduction of column 4 with coincident modifications in the angles of asso- 

 ciated plates is seen in Palaeechinus quadriserialis (p. 307; Plate 30, fig. 3, area C). In L. 

 septies (Plate 45, fig. 1) the fourth column originates on the right of the center in areas A and 

 E, but on the left of the center in areas C, G, and I. The fifth column originates with a 

 pentagon in the middle in all areas. In areas A and E it originates in the sixth row with a 

 heptagon on the right ventral border, in G and I in the sixth row with a heptagon on the left 

 ventral border, and in area C in the seventh row with a heptagon on the left ventral border. 

 The sixth column originates with a pentagonal plate in the tenth or twelfth row in each area. 

 It originates in areas A and G in the twelfth row on the right of the center with a heptagon on 

 the right or left ventral border; also in area C it originates in the twelfth row, but on the left of 

 the center, and with a heptagon on its right ventral border. In areas E and I the sixth column 

 originates in the tenth row, on the left of the center with a heptagon on the right ventral 

 border. The seventh column originates with a pentagonal plate in the middle of each area, 

 with a heptagonal plate on the ventral border. In three cases, areas E, G, and I, the heptagon 

 lies on the right, and in two cases, areas A and C, on the left of the initial pentagon. The 



