284 THE VOYAGE OF H.M.S. CHALLENGER. 



top stem-joint. A few fossil species, however, have been figured or described as not 

 possessing any external basals. Two of these are from British rocks, Pentacrimis fisheri 

 and Pentacrinus dixoni. The former was described by Baily,' who was unable to detect 

 the presence of interradial basals, and was led therefore to regard the first radial s as 

 basals. True basals are really present, however, and may be seen in the original 

 specimen in the Dorchester Museum, or in another found subsequently and now in the 

 possession of Mr. Damon of Weymouth. 



The same is the case with the specimen of Pentacrinus dixoni in Mr. Willett's 

 collection at Brighton, which was figured in Dixon's Geology of Sussex (1878 edition, 

 pi. xix. fig. 22). In both these species, therefore, the supposed absence of basals is 

 really due to error ; and I think it likely that the same may be true both of Isocrimis 

 2)endulus, von Meyer, and of the Forest Marble specimen from Farley in Wiltshire, which 

 was described by Goldfuss^ as Pentacrinvs scalaris ; and also of Pentacrinus penta- 

 gonalis 'personatus from the Brown Jura. According to Quenstedt ^ three pieces rest on 

 the top of the stem " womit jedes der 5 Hauptradiale beginnt." But neither then nor 

 in the Eucriniden did he make any comment on the absence of basals, though he 

 must have noticed it. They may perhaps be small and only just in contact by their 

 central ends, so that they are concealed beneath the radials, as sometimes hapjaens in 

 Encrinus and in the fossil Comatulae.* But it ap23ears to me improbable that the 

 embryonic basals of any Pentacrinus should have undergone transformation into a 

 rosette, as those of many Comatulse do. A St.alked Crinoid with a rosette would be a 

 novelty indeed. 



One would greatly like to know the real condition of the anomalous specimen of 

 Metacrinus costatus represented in PI. XLIX. fig. 2, wdiicli has no basals visible externally. 

 They are generally so very well developed in this genus that their abssnce altogether 

 seems unlikely ; and I suspect therefore that they are quite small and concealed between 

 the top stem-joint and the radial pentagon, as in the case of Encrinus and the fossil 

 Comatulse. 



It is a curious fact that there are so very few species of Pentacrinidaj with only one 

 ray-division, i.e., with only ten arms; while at the same time the number of arms rarely 

 reaches the large total of one hundred or more, as it does in some of the giant species of 

 Actinometra from the Philippines. 1\\ Pentacrinus maclearanus (PL XVI.), Pentacrinus 

 ivyville-thomsoni (Pis. XVIIL, XIX.), Pentacrinus alternicirrus (PI. XXV.), Pentacrinus 

 hlakei (PI. XXXI.), and Pentacrinus decorus (Pis. XXXIV.-XXXVIL), the rays may 

 divide three times, i.e., there may be distichal and palmar axillaries above the radials. 



' Description of a new Pentacrinite from the Kimnieridge, rf. O.xfortl Chy of "Weymoutli, Dorsetshire, Ann. arid 

 Mag. Nat. Hist., ser. 3, vol. vi. pp. 25-28, pi. i. 



2 Petrefacta Germania", vol. i. pi. Ix. fig. 10. 



3 Der Jura, 1858, pp. 363, 364. 



* Jourii. Linn. Soc. Land. (Zool.), vol. xv. p. 195, pi. ix. fig. 6. 



