242 H. Woodward — On a new Silurian Star-fish. 



fragment of its base and one of its first pair of pinnae. On care- 

 fully examining the sides of the arms, where exposed, a few bases 

 of broken off spines can be detected, indicating probably that the 

 arms were originally spinous along their borders. 



At the point m, Fig. 1 a., the madreporiform tubercle can be dis- 

 tinctly seen in situ, occupying the same relative position in the fossil 

 which it does in all the living species of OpMuridce. 



The centre of the body of the animal is marked by a rosette com- 

 posed of five pairs of plates, forming a pentagonal figure, each pair 

 being anchylosed together, and forming at the outer margin a rounded 

 lobe — like the petal of a flower. Between each of these is inserted 

 the base of one of the five arms articulated and united to the pen- 

 tagonal plates by a pair of styliform processes given off from the 

 external margin of each lobe (see s. Fig. la). 



The body appears to have been discoidal, and was probably of 

 considerable thickness, but the hard stony matrix precludes the 

 possibility of ascertaining its extent. We are able, nevertheless, 

 to perceive between the arms several of the pentagonal and hexagonal 

 plates, which formed the covering of the disk, still in situ (see d, d, 

 d, Fig. 1 a, and Fig. 1 c), the surface of which is covered with 

 minute tubercles, several of which near the madreporiform body 

 are elevated into prominent papillao (see p, Fig. 1 h) . 



From the position of the madreporiform tubercle (m) with regard 

 to the central pentagonal plates (c, Fig. la), there is no reason to 

 doubt that these are the true oral plates, and as additional evidence, 

 it will be observed that the arms take their origin from the margin 

 of the pentagonal rosette, and overlie the body-dish, as in all the living 

 OpMuridcB ; the pinnae also take their origin from the same surface 

 of the arms ; the pinnse in the Echinodermata being invariably placed 

 on the innermost border of the arms near the mouth. 



After a careful examination of the bibliography of the class 

 Echinodermata, and a comparison of the fossil under consideration 

 with all those forms of recent and fossil star-fishes likely to aid me 

 in my investigation, I have been led to refer it to the order 

 OpMuridoB. The members of this group are very distinct from the 

 true star-fishes (^Asteriadoe) on the one hand, and the Crinoidece 

 on the other. 



" In fact," writes Prof. Edward Forbes,^ " they hold the same 

 relation to the Crinoidece that the true star-fishes hold to the 

 sea-urchins" (Echinidce). "They are Spinigrade animals, and have 

 no true suckers by which to walk, their progression being effected (and 

 with great facility) by means of five long flexible-jointed processes, 

 placed at regular distances round their body, and furnished with 

 spines on the sides and membranous tentacula. These processes 

 are very different from the arms of the true star-fishes, which are 

 lobes of the animal's body ; whereas the arms of the OpMuridce 

 are superadded to the body, and there is no excavation in them for 

 any prolongation of the digestive organs." 



Of the families Ophiurce and Euryales, included in this order, 

 1 "History of British Star-fishes," p. 19. 



