NO. 3 CASSIDULOID ECHINOIDS — KIER 43 



The tubercles are larger on the adoral surface of the later species 

 than they are on the earlier. In P. depressus (pi. 2, fig. 5) of 

 the Bathonian, and the Callovian Py gurus {Mepy gurus) sp. from 

 Madagascar the tubercles are quite small, whereas in the Albian P. 

 jagueyanus and the Cenomanian P. lampas (pi. 3, fig. 2), they are 

 much larger. There is a trend toward a narrower test, with most of 

 the earlier species such as P. depressus and P. blumenhachi having 

 a wide test with the width exceeding the length, and most of the 

 later having a more elongate test with the length exceeding the width 

 as in P. lampas and P. africamis. However, there are exceptions 

 to this trend, with such species as P. acutus Agassiz from the 

 Bajocian having an elongate test, and P. royeri Cotteau from the 

 Kimmeridgian having a very wide test. 



In general, in later species the test is higher than in the earlier. 

 In the Bajocian species P. acuta and P. terquemi the height is 

 approximately 25 percent of the length, whereas in the Albian P. 

 jagueyanus it is 34 percent and in the Cenomanian P. lampas it is 

 58 percent. 



As discussed above (see p. 10), the petals in the earlier species 

 extend to the margin of the test, but in the later species they termi- 

 nate at a considerable distance adapical to the margin. 



Ecology. — Joysey (1952), in a most interesting paper, has given 

 his interpretation of the ecology of Pygurus hausmanni (Koch and 

 Dunker). From a study of the tubercles and the petals, he has 

 concluded that P. hausinanni lived partially buried with its lower 

 surface completely covered with sediment, and its petals free of 

 sediment. 



Morphology. — On the holotypc, in the Lambert Collection at the 

 Sorbonne, of P. geryvUlicnsis Peron and Gauthier, there are four 

 unusual pores in each phyllode. These pores occur between the edge 

 of the peristome (chart 3, fig. e) and the first pore pairs of the 

 phyllode in the position of buccal pores, and are probably primitive 

 buccal pores. As discussed on page 7, buccal pores, with this one 

 exception, do not occur in the cassiduloids until the Cenomanian, 

 and then usually only in species having single-pored phyllodes. 



M. Collignon very kindly lent me 21 specimens of an undescribed 

 species of Pygurus (Mepygurus) from Madagascar. Most of the 

 specimens are beautifully preserved, showing clearly the plate sutures. 

 It is interesting to note that in some of the specimens the posterior 

 oculars are in contact (text fig. 21) as is typical in the genus, but in 

 others these oculars are separated by one interambulacral plate (text 



