Il8 NEW YORK STATE MUSEUM 



That they do not exist is amply shown by our plates 3 and 9. This 

 author, on the other hand, in his definition of paxillae (19 15, 

 page 16) expresses a paleontological article of faith when he adds 

 " None are known in Paleozoic genera." In his plate 30, however, 

 he gives camera lucida drawings (figures i and 2) of structures 

 which he refers to on page 298 as '"' articular spines and probable 

 paxillae." We shall take pleasure in adding more evidence for this 

 remarkable discovery and in making that w'ord " probable " unnec- 

 essary in this connection. Our plate 4 shows paxillae with three 

 spinelets each ; shows the spinelets in open and in closed positions ; 

 and shows also the articular faces of the pedicels. We are all 

 under the influence of preconceived ideas which make us hold the 

 false as true and the true as false and we are lucky indeed when 

 we succeed in freeing ourselves from a single one of these many 

 bonds. 



Intimately associated with classification is terminology, which is 

 also often a stumbling block in the way of both student and expert. 

 Urasterella gives us a good example. 



Gregory, in 1900, page 250, placed Urasterella under the 

 Phanerozonia, not because it had large marginals but because, 

 when the arm was preserved in open condition and viewed from 

 the oral side, its adambulacrals covered the marginals and hid them 

 from sight. He says (loc. cit.) " The adambulacral plates are large 

 and act as marginal plates." He then immediately confuses his 

 nomenclature and makes marginals and adambulacrals synonymous 

 terms. Speaking of the adambulacrals he proceeds to say, " The 

 axes of the marginal plates are parallel and the rays petaloid (as in 

 Stenaster), or the axes of the marginal- plates are convergent "; etc. 

 The latter statement must be confusing to the student who would 

 like to retain the idea that the two terms apply to radically different 

 elements. It will be seen later that the first statement quoted from 

 Gregory contains a serious error of fact, for the adambulacrals do 

 not function as marginals but rather as cover plates for the food 

 groove (see our plates 8 and 9). True marginals are present and 

 perform their own essential functions with relation to the plates of 

 the food groove. 



Schuchert has a much more accurate conception of the structure 

 of the genus and in 1915, page 172-73, makes a new family for it 

 (Urasterellidae) and places it under the Cryptozonia of Sladen, 

 Even here it can rest but a short time, for in its anatomical struc- 

 ;ure are certain details which it shares with many other Palaeozoic 



