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 eacli axillary united by 

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



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

 raised into a strongly marked keel, wliich 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. 



EvmarJ^s. — The aliove description is based on the examination which I have 

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

 from Nevis, now in the geological department of the British Museum, {b.) 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. ((/.) 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- 

 nic|ue) and Ellis f (Barbados) ; but judging from the figures given by these 

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

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

 Geological Society of London, which is mentioned by both Miller and Mllller if 

 as a I', aqud-medusa', is really referable to Oersted's type P. miillcri, which is so 

 well described in Ltitken's classical memoir. § If the sixth example mentioned 

 by Miillerll 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. 

 Tniilleri. 



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

 distinction. They are well shown in Miller's figu]'e,1[ 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 maikeil indeed ; and it is 

 recognizable, though of course less di:^tinctly 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 Petitacrinidce. 



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 cirri>s-vessels, is united by syzygy to the joint 

 below it, just as in P. miilleri and in all the Pcritacrinidrc ; but this lower or 

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



* Mem. de I'Acad. IJoy. des Sci. Paris, 1755 (published 1761), pp. 228-247, I'l. 

 VIII., IX. 



t rinl. Trans., 1762, Vol. LII. Part I. PP- 357-362, Tab. XITI. 



t Abhandl. d. Berlin. Akad., 1843, p. 185. 



§ Um Vestindiens Pciitacriner, mod nogle Bemaerkninger oni Pentacriuer og .'^iJ'- 

 lier i Alinindelighed. Videiiskab. IMcddel. fra den naturhi&t. Foruu. i Kjobeuhavn, 

 1864, Nr. 13-16, pp. 195-245, Tab. IV., V. 



il Lor. cif. 



H Luc.cit., p. 51, n. II. fig. 5. 



