LEPIDACTIS WENLOCKI. 113 



Genus LEPIDACTIS, novum. 



Generic Characters. — Arms five, petaloid. Adambulacralia wide, nearly all 

 similar. Mouth-angle plates large with distinct odontophor. Distinct rows of 

 supero- and infero-marginalia and radialia. 



This genus is from the Wenlock Limestone of Dudley — the same horizon 

 and locality as Lepidaster grayi. It shows a great general resemblance to Lepi- 

 daster in the shape and disposition of its adambulacralia and mouth-parts and in 

 the position of its madreporite. The five arms and the structure of the marginalia 

 show it, although contemporaneous, to be of a more primitive type. The shape of 

 the madreporite and other points noticed in the description, suggest that it does 

 not belong to the same lineage as Lepidaster, but rather to another offshoot. It is 

 also interesting to note that the structure of the axillary oral region and of the 

 apical surface is parallel to that shown in early " Mesopalaeaster " stages of the 

 Asteroidea dealt with in Section A of this Monograph. 



The genotype and only species is Lepidactis wenlocla. 



1. Lepidactis wenlocki, nov. sp. Plate VI, fig. 5; Text-figs. 68 — 70. 



Material. —Only one specimen, preserved in the British Museum (Nat. Hist.) 

 and registered as 57-126. Originally only the oral surface was exposed, but I have 

 been able to lay bare also the apical surface of the greater portion of one arm. 

 Unfortunately the ossicles have been much disturbed before entombment, especially 

 in the mouth-region. The specimen when found was cracked across the middle 

 and put together again. These disturbances add considerably to the difficulties of 

 study. 



Oral Surface (Plate VI, fig. 5; Text-figs. 68, 69). — The specimen may be 

 orientated from the position of the madreporite (M. of PI. VI, fig. 5). The arms on 

 each side of the madreporite are regarded as numbered i and n, and the number- 

 ing is continued in a counter-clockwise direction. The best reconstruction of the 

 arm can be made from arm in and the neighbouring right interradius (Text-fig. 

 68). This interradius is occupied by two large infero-marginalia and an odonto- 

 phor. The latter plate is completely shut off from the margin, and the axillary 

 structure is consequently strongly reminiscent of the early " Mesopalaeaster " stage 

 of the Family Promopalasasteridge (compare Text-fig. 41, p. 82). The odontophor 

 on the left side of the arm is not shut off from the margin, but here the plate has 

 obviously been much displaced and has one of its bordering infero-marginalia 

 missing. This odontophor has the whole of its flat shield-shaped surface exposed. 

 The proximal extremity is sharply pointed, the point doubtless fitting into the 

 concavity between the two mouth-angle plates. On each side of the median point 



