AET. 20 



A RARE CRETACEOUS SEA URCHIN REESIDE 



The writer believes tliat tlie genus ScuteUaster may fairly be regarded as a 

 -synthetic, or generalized, type from which have been evolved Scutella on the 

 one hand and Clypeaster on the other. 



In the present condition of the type, as shown by the retouched 

 photograph forming figure 1 of plate 1, some of the details noted 

 by Cragin are not evident. The ambulacral petals are entirely 



< /of \t\ \ 



Fig. 2. — Compari.sox of Arrange.mext of Plates of (B) AcriNAri Sidej of Scutella 



SUBROTUXDATA Lam.^ECK WITH THAT OF (A) SCUTELLASTER CrETACEUS CEAGIX. THE 



Letters Indicate the Equivalexts as Interpreted by the Writer. Peristome=P. 



missing, and it is possible only to guess at their probable maximum 

 length and breadth. The original surface of most of the plates is 

 gone and in only a few small areas is anything suggesting the spines 

 or tubercles present (see pi. 1, fig. 2). No part of the ambitus is 

 preserved, and any statement as to the outline of a complete test 

 is unfounded. To all appearances the outline of the specimen is 

 as it was when originally found, and Cragin was probably unjusti- 



