NO, 3 CASSIDULOID ECHINOIDS — KIER 9 



series. The phyllodes of the Kimmeridgian P. (Py gurus) perreti 

 Lambert (chart 3, fig. f ) and of the Neocomian species P. (Pygurus) 

 rostratus (Agassiz) (chart 3, fig. g) are similar, being broad and 

 having three series of pore pairs in each half -ambulacrum. In the 

 Neocomian P. (Pygurus) montmollini (Agassiz) (chart 3, fig. h) 

 the phyllodes have evolved to just two series of pore pairs in each 

 half -ambulacrum. By Albian and Cenomanian time there is only one 

 series as in P. (Pygurus) jagueyanus Cooke (chart 3, fig. i), P. 

 (Pygurus) lampas (De la Beche) (chart 3, fig. k) and P. (Pygurus) 

 africanus De Loriol (chart 3, figs. 1, m). It is interesting to note that 

 in one of the phyllodes of one of the specimens of P. africanus figured 

 by Dc Loriol there is a very short inner series. In P. (Pyguropsis) 

 noetlingi De Loriol (chart 3, fig. j) there are two to three series of 

 pore pairs but only for a short distance, with a single series near the 

 peristome. 



In the nucleolitid type phyllode, there is not the same evolutionary 

 trend from the Bajocian to the Cenomanian as that found in the 

 pygurid type. As can be seen on chart 2, where the phyllodes of 24 

 representative species are figured, the Lower Cretaceous phyllodes 

 are very similar to those of the Middle Jurassic (Bajocian). Through- 

 out this period all the species, except for Ochctes morrisii (Forbes) 

 (chart 2, fig. M) have two series of pore pairs in each half-ambula- 

 crum. The phyllodes of six species of Nuclcolites (chart 2, figs. A, 

 B, C, D, F, G) are very similar even though they do not occur at the 

 same time. Even phyllodes of different genera are basically similar 

 as shown in Bothryopneusfes (chart 2, fig. E), Pseudosorella (chart 

 2, fig. H), Pygorhynchus (chart 2, fig. I), Plagiochasma (chart 2, 

 fig. L), Phyllohrissus (chart 2, fig. K), and Clypeopygus (chart 2, J). 

 However, during and after the Cenomanian the number of pores in 

 each plate is reduced from two to one, as described above, and buccal 

 pores appear. In the Turonian, most of the species have moderately 

 widened phyllodes with two series of pores in each half-ambulacrum 

 such as in Pctalohrissus (chart 2, fig. R) or Parapygus (chart 2, fig. 

 S). From this time through the Senonian there is an evolutionary 

 trend in many genera toward a widening of the phyllodes, and a 

 reduction in the number of pores in each inner series, such as in 

 Hardouinia (chart 2, fig. T) and Pygidiolampas (chart 2, fig. U). 

 This trend in Hardouinia is described in detail on page 146. In the 

 Tertiary and Recent genera there is a relationship between the size of 

 the test and the number of pores in the phyllode. Genera with small 

 tests such as Pliolampas (chart 2, fig. V) and Cassidulus (chart 2, 



