20 THE APODOtJS HOLOTHTJEIANS 



as a matter of fact both are synonyms of Cuvier's Molpadia. Although Cuvier's 

 diagnosis is very brief and is also erroneous, there can be no doubt that the 

 animal he had in hand was a specimen of what has since been called Trocho- 

 stoma; for he says it was from the Atlantic Ocean, and none of the other 

 genera to which his description might apply occur there. If we do not use 

 Molpadia in this sense, it cannot be used at all, and the name of the family 

 would consequently have to be changed. Since I have no doubt as to the group 

 of holothurians to which Cuvier intended to apply Molpadia, I should not con- 

 sider myself justified in rejecting his name. 



As regards the remaining genera we are in difficulty, because of the very 

 incomplete characterization given them by their original describers and the sub- 

 sequent extensive emendations of later writers. The loss of the type specimens 

 increases the trouble. The small genus Eupyrgus is the best characterized of all 

 and seems to be a natural group. In 1840, Grube described Haplodactyla, a genus 

 which he characterized as having simple tentacles without digits. Curiously 

 enough, as Ludwig has shown, his type seems to have been a specimen of 

 M. musculus Risso, and consequently Haplodactyla is a synonym of Molpadia. In 

 1868, Semper described a holothurian to which he very naturally applied the 

 name Haplodactyla, but unfortunately Grube 's name cannot be so used, if we 

 are to observe the modern rules of zoological nomenclature, and consequently 

 Semper 's species and its allies are without a generic name. As the tentacles 

 lack digits, we may call the group Aphelodactyla. In 1841, Gould described, 

 under the name Chirodota arenata, a remarkable holothurian from the coast of 

 Massachusetts, which Stimpson ( '53) later made the type of a new genus Cau- 

 dina. Unfortunately, Stimpson makes no attempt to define this genus or to show 

 how it differs from Molpadia, referring simply to Ayres' ('52a) description, 

 which contains some glaring errors. However, owing to the type species being 

 well known, Caudina has been very generally accepted, and several other species 

 have been added to the genus. In 1850, Miiller described an interesting holothu- 

 rian which he called Molpadia chilensis, and in 1868 Semper added M. australis. 

 The latter gave a revised diagnosis of the genus, based on his own and Miiller 's 

 work, and widely different from the original one of Cuvier. As defined by 

 Semper, Molpadia was distinguished from Caudina chiefly by the presence of 

 "retractor" muscles. As that character is one of very doubtful importance 

 among the apodous holothurians (see pages 52 and 144), the species included by 

 Semper and later writers in Molpadia belong rather in Caudina. One impor- 

 tant exception to this statement must be made, however, for Sluiter's (:01) 

 species, M. demissa, is evidently quite unlike the others, and must be made the 

 type of a new genus, which may well be called Acaudina, from the absence of a 

 caudal appendage. 



