152 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Contains : 



P. primseva (Forbes). Ludlow of England. 

 P. bonneyi Gregory. Ludlow of England. 

 P. (?) ramseyensis Hicks. Tremadoc of Wales. 



For other remarks see Palseostella. 



Since the foregoing was written, Schondorf 's work cited above has 

 come to hand. He studied wax squeezes of P. primseva and deter- 

 mined that the genotype is devoid of marginalia, and therefore refers 

 Palasterina to the Cryptozonia. He writes: " Special marginalia ap- 

 pear not to be present, at least the marginal rows are in no way dis- 

 tinguishable from the other intermediary [accessory interbrachial] 

 plates. Accordingly Palasterina primseva Forbes sp. does not belong 

 as stated by Gregory (p. 349) to the asterids with distinct marginal 

 plates, the Phanerozonia, but with the asterids having inconspicuous 

 or no marginalia, the Cryptozonia' 7 (p. 222). 



The present writer holds that there are inframarginalia present all 

 along the edge of the interbrachial areas and the rays, and that they 

 are most typical along the distal portion of the rays. Here the 

 inframarginalia are ontogenetically youngest and less affected by 

 subsequent growth displacement and alteration than are the older 

 ones in the interbrachial areas. In the latter region it is true that 

 the marginalia are not conspicuous, but so long as one can make 

 them out to be inframarginalia, size alone can not be the criterion 

 that will permit of the conclusion that no marginalia are present in 

 Palasterina. However, the difference in interpretation between 

 Schondorf and the writer is not a great one, as neither lays great 

 taxonomic value on whether the marginalia are prominent or u not 

 prominently developed" (p. 223). So long as the inframarginalia are 

 more or less prominent, one of the generic characters of Palasterina, 

 a phanerozonian, is present, and when they are so inconspicuous as 

 not to be made out among the other ossicles, we have one of the 

 generic characters of Schuchertia, a cryptozonian. 



Schondorf also states that the ambulacralia, and the adambulacralia 

 as well, are all opposite and do not alternate with one another. The 

 present writer states that the ambulacrals are " slightly alternating, " H 

 and throughout this work he has given the arrangement of these 

 ossicles his special attention. In a great many cases, and especially 

 in the Ordovicic species, he has had difficulty in ascertaining what 

 was their actual position in the living animals, for nearly all the 

 fossils have been squeezed more or less. He has always given their 

 arrangement as they impressed him in the fossil when no evident dis- 

 tortion could be seen. The writer would not lay special stress upon 

 slight alternation among the ambulacralia, for in many Ordovicic 

 species there is some variation in each ray from opposite to slightly , 

 alternate. Of course, when the alternation or opposite arrangement 



