162 Herbert L. Hawkins — Studies on the Echinoidea, etc. 



Unfortunately, the two specific names most familiar to British 

 geologists ("P. semisulcatus " and "P. umbrella") have to be 

 changed. The impersistence of palseontological nomenclature is 

 a source of considerable difficulty to students and teachers, and of 

 ironical amusement to those less intimately affected. The trouble is 

 aggravated by the fact that abundant and early known species reflect 

 most frequently the flickering light of systematic research. Realizing 

 to the full, by personal experience, the gravity of the confusion 

 caused by such changes, I sought long for a loophole through which 

 the current nomenclature could be thrust. But I am convinced that 

 there is none. A. shelving of the matter would only postpone the 

 inevitable rectification, and meanwhile involve the whole subject in 

 greater confusion. If the truth will out, then the sooner the better. 

 With the hope of making this unpleasant change final, I have studied 

 and catalogued upwards of 400 papers that had any bearing, however 

 remote, upon the question. As a result I feel confident that no 

 further alteration, depending upon past literature, will be necessary 

 for any who are willing to follow logically and impartially the laws 

 of nomenclature. No excuse is necessary for the amount of space 

 devoted to this least inspiring aspect of the forms to be discussed, 

 since it can there be seen on what evidence the changes are made ; 

 and, if any error or omission occurs, speedy correction can be made. 



In respect of the generic classification, no essential modifications 

 are introduced. The scheme adopted by me in 1912 (Proc. Zool. Soc.) 

 seems adequate, as far as concerns the family under review. Apart 

 from alterations in nomenclatui'e, to be discussed later, the chief 

 difference in the present arrangement lies in the elevation of the 

 subdivisions, previously suggested as subgenera of Pygaster, s. lat., to 

 the rank of independent genera. The reasons for this change cannot 

 be considered here, but will, I believe, obtain justification when their 

 morphological basis is published. 



2. The Type oe Pygaster, Agass. 



The genus Pygaster was founded by Agassiz in 1836 (Prodrdme) 

 to include two species, Cli/peus semisulcatus, Phillips, and Nucleolites 

 depressus, Miinster in Goldfuss. The species were mentioned in this 

 order, and, since the former conforms more closely to the brief 

 diagnosis first given, it must be regarded as the genotype. Nucleolites 

 depressus is an entirely different form. In 1839 Agassiz, giving the 

 first full description of the genus, accompanied by that of several 

 species, omitted to include either of the forms for which he had 

 originally proposed it. He stated {Ecli. Suisse, p. 80) that he knew 

 of six species, three from the Cretaceous and three from the Jurassic. 

 Of the Cretaceous types, Macropygus truncatus was probably one, and 

 Anorthopy gus orbicularis may have been another, but a third was 

 never described by him. Four Jurassic species are recognized in the 

 work, in spite of the reference to three only in the generic discussion ; 

 they are P. laganoides, P. patelliformis, P. tenuis, and P. umbrella. 

 There is thus no reference to the genotype. When the name 

 semisulcatus reappears (Desor, Won. Gal., 1842) it is found as 

 a synonym of " P. umbrella ". The dire confusion that subsequently 



