MUSEUM OF COMPARATIVE ZOOLOGY. 169 



usually 6-8. Tertiary arms of 6-14 joints, and occasionally another division 

 after 8 or 10 joints more. The first two joints after each axillary united by 

 syzygy, with a pinnule on the epizygal. No other syzygies on the arms. 



The joints of the large pinnules on the arm-bases have their distal edge 

 raised into a strongly marked keel, which projects forwards over the base of the 

 next joint. This feature recurs on all the pinnules of the arms, though it is 

 less distinct in their middle and outer portions. 



Remarks. — The above description is based on the examination which I have 

 made of the following examples of the type: — (a.) Miller's original specimen 

 from Nevis, now in the geological department of the British Museum. (6.) One 

 dry specimen and another in spirit, both in the zoological department of the 

 same Museum, (c.) One dry specimen in the Hunterian Collection of the Royal 

 College of Surgeons, (d.) Two dry specimens obtained by Dr. Carpenter and 

 Sir Wyville Thomson from Mr. Damon of Weymouth. 



I have not seen either of the individuals described by Guettard * (Marti- 

 nique) and Ellis f (Barbados) ; but judging from the figures given by these 

 authors I have little doubt that they belong to the type which is now generally 

 known as P. asteria. The specimen from Guadeloupe in the Museum of the 

 Geological Society of London, which is mentioned by both Miller and Muller J 

 as a Pi caput-medusee, is really referable to Oersted's type P.miilUri, which is so 

 Avell described in Liitken's classical memoir. § If the sixth example mentioned 

 by Muller || be the one formerly belonging to the Natural History Society at 

 Copenhagen, and bought in 1846 by the University Museum, it is also a P. 

 miillcri. 



The peculiar features of the pinnules of P. asteria afford an excellent specific 

 distinction. They are well shown in Miller's figure,!" which represents a pin- 

 nule some little way out on the arms. In the lowest pinnules the tubercular 

 projection at the distal end of each joint is very marked indeed ; and it is 

 recognizable, though of course less distinctly so, all along the arms ; so that 

 arm fragments of this species can be readily identified, which is more than can 

 be said for most of the Pentacrinidce. 



The stem also, like the arms, has a definite character of its own, which has 

 not always been correctly described. The nodal joint, i. e. that which is 

 pierced by the canals lodging the cirrus-vessels, is united by syzygv to the joint 

 below it, just as in P. miillcri and in all the Pcntacrinidtr ; but this lower <>r 

 hypozygal joint is not grooved externally for the reception of the thick basal 



* Mem. de l'Acad. Roy. des Sci. Paris, 1755 (published 1761), pp. SB8-847, Pi 

 VIII., IX. 



t PhiL Trans., 1762, Vol. LII. Part I. pp. 357-362, Tab. XIII. 



J AbhandL d. Berlin. Akad., 1843, p. 185. 



§ Om Vestindiens Pentacriner, med nogle Bemaerkninger nun Pentacriner og - 

 lier i Almindelighed. Videnakab. MeddeL fra dan n a tnrhw t Form, t gjSbea 

 1864, Nr. 13-16, pp. 196-846, Tab, IV., V. 



II Loc. cit. 



H Loc. cit., p. 51, PI. II. fig. 5. 



