30 



ASTEROIDEA. 



the spines are arranged thereon ; Pteraster having combs of spines united by a mem- 

 brane on the inner row of plates, and long, stiff, fin-like spines on the outer row, 

 whilst Palaocoma has the outer row spinigerous, and the inner row destitute of these 

 appendages. The three species of Palmcoma described by Mr. Salter, and the two sub- 

 genera, Bdellacoma and Rhopalocoma, were all obtained from the Lower Ludlow Rocks at 

 Leintwardine. 



Palaocoma Marstoni, Salter. Ann. and Mag. Nat. Hist., vol. xx, p. 328, pi. ix, fig. 3. 



Fig. 17. 



Arms lanceolate, obtuse at the apex, united throughout by a delicate reticulate mem- 

 brane clothed with spines ; mouth opening wide, angle ossicles double ; ambulacral 



grooves narrow, and bounded by two rows of small, quad- 

 rate ossicles ; the margins of the rays are formed by two 

 series of adambulacral plates, armed with regular oblique 

 combs of long rigid spines, which form a conspicuous spinous 

 fringe on the margins of the arms. Mr. Salter says, " that 

 shorter spines, set at a wide angle from the margins of the 

 arms, distinguish this from the next species. The beautiful 

 and delicate web-like disc between the arms bears short 

 spines also; it is sometimes expanded, as in fig. 17, but 

 more generally contracted, so as only to make the arms a 

 little broader, and give it a blunt appearance. The mouth 

 is wide, of a true pentagonal shape, and with rather strong 

 bordering plates, of which the triangular adambulacral plates are most conspicuous. The 

 calcareous stellate spiculse which dot over the thin disc are easily seen through the opening 

 of the mouth." 



Palasocoma Marstoni, Salter. 



Locality. — Church Hill, Leintwardine, Shropshire, in Lower Ludlow Rock. 



Palaocoma Colvini, Salt. Resembles the preceding species, but is remarkable for the 

 length of its hair-like spines, which exceed those in any known star-fish, recent or fossil ; 

 it is found with the preceding. 



Palmcoma Cygnipes, Salt. Arms elongate, marginal spines short, inter-brachial mem- 

 brane delicately expanded, mouth opening small ; found associated with the preceding. 



Mr. Salter forms sub-genera of two other species belonging to this group, which 

 present characters differing from other PalcBOComce. 



