Species of British Echinodermata. 117 



Genus XI. Luidia, Forbes. 

 {Luidia, Forbes, 1839; Hemicnemis, Midler & Troschel, 1840.] 

 Rays 5-7, very long, narrow at the base, and of nearly equal 

 diameter throughout, together with the disk flat above, and 

 covered in every part by closely aggregated paxillse. A single 

 row of lateral ray-plates, which, together with the whole under 

 surface, are covered with slender, acute spines. Suckers biserial. 

 No anus. Madreporiform tubercle near the margin of the disk. 

 A single row of pedicellarise alternating with pores in a groove on 

 the exterior side of the adambulacral plates. Respiratory pores 

 very numerous. 



It has always hitherto been stated that this genus was unpro- 

 vided with pedicellarije. Such a statement, however, is incorrect. 

 These remarkable organs are present, and hold, moreover, an iso- 

 lated and peculiar position, which, I believe, is without a parallel 

 among other Echinodermata. If the oral surface of a Luidia be 

 carefully examined, there will be found on either side of the ambu- 

 lacra, and midway between the ambulacra and the margin of the 

 rays, or, in other words, exterior to the adambulacral plates, a 

 longitudinal row of pores situated in a sulcus; and, crowning 

 each of the calcareous rib-like plates which separate these pores 

 from each other, there will be observed a single, erect, triangular, 

 pincer-formed pedicellaria. It is not a little remarkable that 

 these organs, which are by no means inconspicuous, should have 

 apparently wholly escaped the observations of Von Diiben and 

 Koren (who give a carefully executed figure of a section of the 

 under surface of a ray of Luidia Sarsii) and of Sars, who, in his 

 ' Middlehavets Littoral Fauna/ draws the specific character in our 

 two species from the number and form of the spines of the ad- 

 ambulacral plates, which, as we have seen, are immediately 

 adjacent to the avenues in which the pedicellarise are situated. 

 The pedicellarise themselves are organs which we find to afford 

 valuable specific distinction in this genus. In Luidia Savignii 

 they are short, broad, and tumid — in fact, in the form of a 

 nearly equilateral and equiangular triangle ; while in Luidia 

 Sarsii they are much more elongated, narrow, and not tumid, 

 and have the outline of a somewhat produced isosceles triangle. 

 The peculiar position which the pedicellarise occupy in this genus 

 will, we doubt not, form almost necessarily a ground of argu- 

 ment with those naturalists who shall hereafter discuss the 

 nature of the functions which these anomalous and peculiar ap- 

 pendages of the Echinodermata discharge. 



Luidia Savignii (Audouin). 



1828. Asterias Savignii, Audouin; Savigny, Histoire de l'Egypte, pi. iii. 

 (1809); description (1828), vol. xxiii. p. 9. 



