TRANSACTIONS OF SECTION C. 333 



The latter part of the paper describes a quarry of the Old Red Sandstone in 

 Monmouthshire, containing apparently an abundance of comminuted vegetable 

 remains, and also several specimens of pteraspis, one of which he believes to be 

 new. 



4. On the Nomenclature of the Plates of the Crinoidal Calyx. 

 By P. Herbert Carpenter, M.A. 



According to the present system of nomenclature there are two distinct sets 

 of plates in the calyx of the Crinoids, to which the name bascds is given. In 

 Platycrinus, and in all those forms in which there are only two sets of plates in 

 the calyx, the upper set were called radials by Miiller, while he termed the lower 

 set, resting on the upper stem segment, the basals. This was perfectly correct, for 

 their position is interradial, and they correspond in every respect to the basals of 

 Pentacrinus, the calyx of which genus was taken by Miiller as a type on which 

 he based his analyses of the calyx in all the other Crinoids. 



In Cyathocrinus, however, there are two rows of plates below the radials, and 

 the plates in the lowest of these were called basals by Miiller because they rest on 

 the upper stem-joint. Nevertheless, they are not homologous with the basals of 

 Pentacrinus and Platycrinus, because they are radial in position. But intervening 

 between them and the radials is a second set of plates (the so called parabasals or 

 subradials), which alternate with both series, and are therefore interradial. I 

 regard these plates as the true basals, while the lower (radial) set are homologous 

 with the under basals of JEncrinus, which were discovered by Beyrich. They are 

 absent in the Apiocrinidae, except perhaps in A. Murchisonianus, in all the recent 

 species of Pentacrinus and in most of the fossil species, but they occur in P.iriareus 

 and in P. subangidaris, where they have been wrongly described as the basals. 

 This name, however, really belongs to the next series of plates, the so called para- 

 basals, or subradials, which are inter-radial like the basals of P. caput medusae, and 

 pierced like them by bifurcating canals, so that there is no doubt as to the homology 

 of the two series. 



The American palaeontologists have sometimes followed Beyrich and some- 

 times followed Miiller in their system of nomenclature. For example, Heterocrinus 

 has two rows of plates below the radials which are variously called (1) subradials 

 and (2) basals, or (1) basals and (2) sub-basals. The relative positions of these 

 two rows are always the same, the upper (subradials or basals) being interradial, 

 and the lower (basals, or sub-basals), being radial. As the former (interradial) 

 series represents an important element in Echinoderm morphology, being homo- 

 logous with the (likewise interradial) genital plates of the urchins and star-fishes, 

 and is also of great morphological importance in the Crinoids themselves, it is 

 very desirable that it should always bear the same name ; and also that this name, 

 basals, should not be used for plates which are neither interradial in their position 

 nor constant in their occurrence. Similarly-named parts are usually supposed to 

 be homologous ; but if we give the same name to plates which are radial in one 

 species and interradial in another, we disregard the principles of homology 

 altogether, and introduce unnecessary confusion into the study of echinoderm 

 morphology. 



Beyrich has already remarked on this and has led the way towards a more 

 rational and scientific nomenclature, by introducing the name ' under-basals ' for 

 the radially situated plates which occur beneath the true basals of Encrinus. 



If it be objected that these under basals, resting as they do upon the upper 

 stem-joint, form the true base of the calyx, let us retain the name basals for this 

 radial series, and call the upper (interradial) series the sub-radials, as is generally 

 done at present. This, however, would necessitate our discarding the name basals 

 altogether for such forms as Pentacrinus caputmediisae, &c, and, as it was first 

 used for the lower row of plates in the calyx of this species, such a step would 

 be inconvenient. The fact remains that the lowest part or base of the calyx is 

 formed in some Crinoids by interradial, and hi others (the minority) by radial 



