Herbert L. Hawkins — Studies on the Echinoidea, etc. 163 



befell the nomenclature of two important species is dealt with in 

 the next section. 



For the present purpose it is sufficient to note that there exists 

 such a species as Pygaster semisulcatus, figured by Phillips (Geol. 

 Yorhs.) under the name of Clypeus, though not described by him ; 

 and that it was originally found, and may yet be collected, in the 

 Coralline Oolite of Malton. This form must, then, represent the 

 type of Pyg aster, the Inferior Oolite species to which the name has 

 been most frequently applied, being here regarded as not even 

 congeneric. Pygaster, with its restored genotype, will include three 

 of the four species described by Agassiz in 1839 — P. patelliformis, 

 P. tenuis, and "P. umbrella" — and so may be taken as expressing 

 most adequately the original meaning of its author. It will absorb 

 the subgenus Ifegapygus proposed by me in 1912, that name having 

 been given in ignorance of the real meaning of the term " P. semi- 

 sulcatus". 



3. The Name Pygaster semisulcatus, Phillips, sp. 



The name Clypeus semisulcatus was given in 1829 by Phillips 

 (Geol. Tories.) to a species from the Coralline Oolite of "Malton, 

 Scarborough, and Wiltshire". No description was published, but 

 a recognizable figure (reduced in size and obliquely adapical in view) 

 was printed. Forms conforming in character to that figured may 

 still be found at the first locality mentioned, and, since no other 

 echinoids at all similar occur there, no doubt can exist as to the 

 species intended. The actual specimen used for the drawing cannot 

 be traced, and has probably suffered the fate of many of Phillips' 

 types. The absence of a holotype is particularly unfortunate, since 

 much confusion surrounds the application of the name. As will be 

 seen later, it is necessary to select a specimen as a lectotype. 



In 1836 Agassiz included C. semisulcatus in his new genus of 

 Pygaster, of which it must be regarded as the type. He would 

 appear to have been guided solely by the figure published by Phillips. 

 In 1839 Agassiz refers presumably to this species (J?ch. Suisse, p. 79). 

 Apart from a casual reference, however, P. semisulcatus does not 

 appear in the work, and, to judge from the evidence available, 

 Agassiz must have considered it synonymous with one of the species 

 there diagnosed, probably with P. umbrella. Desor, in 1 842, was 

 more explicit (Mon. Gal., p. 77), inserting the name in the list of 

 synonyms of P. umbrella. On p. 76 he says that C. semisulcatus 

 "pourrait fort bien n'etre autre chose qu'un jeune de notre 

 P. umbrella ". Since Phillips' figure was, according to Forbes, two- 

 thirds the size of its original, the dimensions of the Yorkshire 

 specimen will have been not far short of those of the Swiss 

 P. umbrella, their identity being thus rendered more possible. It is 

 necessary, then, in view of the conceivable identity of Clypeus 

 semisulcatus, Phill., and Pygaster umbrella, Agass., 1839, to discuss 

 briefly the justification for the former name. Obviously, if the two 

 names apply to the same species, that of Agassiz, supposed to be 

 derived from Lamarck (1816) and perhaps from Leske (1778), would 

 have priority. 



