BEM:SIOiSr OF PALEOZOIC STELLEROIDEA. 87 



Hall tliouglit of basing the genus Argaster, but he does not character- 

 ize it nor even mention that the name in parojithesis is intended 

 as a new tenn wath Asterias antiqua Troost as the genotype. Tliis 

 species, lUce all other Paleozoic starfishes, has double columns of 

 ambulacral plates. This the specimen clearly demonstrates on 

 the edge of the slab where the distal parts of the rays are broken 

 awa}". Argaster should therefore be regarded as a nomen nudum, and 

 should A. antiqua prove to be a Mesopalxaster, it should not be 

 made to displace this genus. 



Asterias antiqua has about 15 inframargiiial plates in each column 

 and about 32 in each adambulacral column. Two of the latter plates 

 meet as usual in a pair of triangular oral armature pieces. 



Each axil is occupied by two large, quadrangular, basal ijiframar- 

 marginal plates. Between these proximally there is a large, widely 

 triaiigular, interbrachial plate the apex of which may or may not 

 attain the margin. Proximal to each axillary interbrachial plate 

 and between the fom- or five pairs of axillary adambulacral plates, 

 there is in the specimen an open space in each of the five areas. 

 What additional plates, if any, occupied this area is not determinable. 

 It may be that the axillary interbrachial plates occupied the entira 

 interbrachial areas and that the present hiatus is due to the worn 

 condition of the specimen. This appears to be the most natural 

 interpretation as it is the nonnal interbrachial stmctiu'c of Mesopa- 

 Iseaster. In Promo palseaster there are always two, three, five, or seven 

 interbracliial margitial plates in each area, a fact wliich excludes Aste- 

 rias antiqua from that genus. 



The abactinal area is not visible, but many of these plates are 

 squeezed beyond the inframarginals, showing the presence of num- 

 erous small plates recalling Mesopalseaster and Promopalxaster. 



Formation and locality. — Troost's label reads: ''Lower limestone 

 on Harpeth River, Davidson County, Tennessee." His manuscript 

 reads: ''It was found * * * on Harpeth River, Davidson 

 Comity, Tennessee. Associated with Spirifer lynx [PlatystropTiia 

 hijorata], CyatJiopJilyJlla [ = Streptelasma], Ortliis [testudinaria], etc." 

 This is apparently the same horizon as that about the city reservoir 

 in Nashville, which is now regarded as of Upper Trenton (Catheys) 

 age. The specimen is in the United States National Museum. 



Cat. No. 39914, U.S.N.M. 



MESOPAL.EASTER(?) PARVIUSCULUS (Billings). 



Plate 9, fig. 1. 



Palseaster parviusculus Billings, Canadian Nat. and Geol., vol. 5, 18G0, p. 69, 

 figure. — Dawson, Acadian Geology, 2d ed., 18C8, p. 594, fig. 197.— Hudson, 

 Bull. N. Y. State Mus., No. 164, 1913, pis. 1-4. 



Original description. — "The si^cchnen is about six lines in diameter. 

 The rays are two lines in length and one and a half in width at the 



