Herbert L. Hawkins — Studies on the Echinoidea, etc. 167 



Eor the species from the Inferior Oolite, so long miscalled 

 P. semisulcatus, the name Clypeus ornatus, Buckman, 1844, is 

 available. This has clear priority over the only other specific name 

 applied to the species during the period of its recognition (P. brevifrons, 

 M'Coy, 1848). This form must in future be known as Plesiechimis 

 ornatus, Buckman, sp. 



4. The type of Plesiechinus, Pomel. 



This genus was proposed in 1883 by Pomel, to include those species 

 of Pygaster whose characters show the nearest approach to those of 

 the Pegular Echinoids. Three of such species were mentioned by 

 him: P. " mega&toma", Wright, P. semisulcatus, "Wright," and 

 P. speciosus, " Quenst." One of these three must be the genotype. 

 P. speciosus, " Quenst.," the last mentioned, is by no means well 

 known (supposing it to be the Nucleolites speciosus of Groldfuss), and 

 may not belong to the Pygasteridse. The name P. semisulcatus, 

 "Wright," refers to the most abundant and best-known species of 

 the three, but unfortunately it is not the true P. semisulcatus (Phill.). 

 It would be confusing to implicate the generic name in the systematic 

 turmoil surrounding the species. The choice will fall, therefore, 

 upon P. " megastoma" , Wright. In spite of its author's doubts as 

 to its separation from his P. semisulcatus, the two species are quite 

 distinct, in both characters and horizon. The appropriateness of the 

 choice is enhanced by the fact that the apical system, on the structure 

 of which Pomel based the genus, is best known in this one of the 

 three species. 



Some discrepancy in the spelling of the name of the genotype has 

 occurred, owing to the printing of no fewer than three different 

 versions by Wright at the time of its first appearance. Of these, 

 macrostomus (Wright, Pal. Soc, Ool. JEch., p. 424), although the first 

 in order, may be dismissed as barbarous and probably accidental. 

 There is little to choose between the two other renderings, macrostoma 

 and megastoma, in respect of their etymology, but since the former 

 accompanies the description of the species, and is several times 

 repeated (loc. cit., pp. 463, 464), it has a technical advantage over 

 the latter, which is employed only on the legend to the plate. 

 Moreover, the name macrostoma has been adopted by authors generally 

 (with the exception of Pomel), and so may be stereotyped as the 

 correct designation of the species. 



The genus Plesiechinus was either rejected or ignored by writers 

 from the time of its publication until 1912, when I provisionally 

 adopted it (Geol. Mag.) on grounds similar to those that caused its 

 proposal. Later in the same year (Proc. Zool. Soc.) I rejected the 

 name on systematic considerations, but retained the division under 

 the name of Pygaster s.str. This was due to a misconception of the 

 meaning of the name P. semisulcatus (the genotype of Pygaster, 

 Agass.). Having recognized that the P. semisulcatus of authors later 

 than 1850 is entirely different from that -of previous writers, and 

 belongs to a different genus, I have been compelled to retain the 

 generic name Pygaster for the former type, so that the name 

 Plesiechinus can be revived for the latter. 



