168 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Tetraster another Cryptozonia form ( Urasterella girvanensis, new 

 species), but also by confusing with their genotype specimens that 

 certainly have the character of Palxaster so far as six columns of 

 actinal ossicles are concerned. This latter admixture the wi'iter has 

 taken out of the genotype and has described it in this work as Hudson- 

 aster hatheri. The adjusting of this matter has been made possible 

 through the kindness of Dr. Bather, who made for this work wax 

 squeezes of the various specimens. After seeing these and the other 

 material originally referred to Tetraster by Nicholson and Etheridge, 

 their various drawings became clear. Their figures are fairly good, 

 but in places do not bring out all the characters, but it was the 

 mixture of three generic forms under Tetraster that made it for a time 

 impossible to determine on what the genus should stand. 



Emended description. — Small, five-rayed asterids, R = about 5 mm., 

 r = about 2 mm. Abactinal side unknown, Actinally convex and 

 in its general expression reminding much of living species with large 

 marginals, but in Tetraster the comparatively massive margining 

 plates are adambulacralia. 



Adambulacrals compose the entire outer actinal areas of Tetraster 

 and margm the entire animal. Distally the pieces are small and the 

 12 ossicles of each column increase rapidly in size with the largest 

 basal pieces of adjoming columns making the prominent interbrachial 

 areas. Ambulacrally all are somewhat excavated, stand high above 

 the furrow and each ossicle terminates m a ridge that joins those of 

 the ambulacrals. All of these plates are abundantly granular. 



Ambulacral furrows not wide but rapidly becommg very deep 

 proxmially, with excavated adambulacral sides. The columns meet 

 in front of the two largest interbrachial adambulacrals. Podial 

 openings are large and issue deeply from beneath the adambulacrals 

 and between the lateral sutures of the ambulacraHa. The pieces of 

 the ambulacral columns are as many as there are adambulacrals and 

 are placed directly opposite one another. Medially the ambulacraHa 

 are elevated, roof-hke, and without a central gutter. 



While the abactinal area is unknown, it appears that the adambu- 

 lacrals also margin this side of the animal. The nature of the skele- 

 ton inside of these columns may be of small pieces as in Urasterella, 

 or, what seems more probable, consist of large radial and supramar- 

 ginal ossicles, without accessory pieces. 



Spines of any kind arc unknown. 



GenoJiolotype. — Tetraster wyville-thomsoni Nicholson and Etheridge 

 as above emended. T. (?) imlricatus (Salter) is also placed under 

 this genus for the present. 



Tetraster as now defined is so distmct in its great adambulacral 

 development that it will not be confused with any other Paleozoic 

 genus except Stenaster. Both genera, so far as the actinal area is 



