CNKMIDACTIS GIRVANENSIS. 161 



other species of Palaeozoic Asterozoa has already been referred to (p. 33). The 

 amount of fusion is not constant in all the specimens. Thus there is a distinct 

 median suture in both D. 103 and D. 255. 



Description of D. 255 (Plate XIII, fig. 1). — D. 255 is a small young specimen 

 of the species which deserves special mention, showing only the apical aspect. The 

 chief points are : (1) The ambulacralia of the mouth-region are not fused across 

 the middle line ; (2) the odontophor in side view is highly swollen and grooved 

 throughout its entire length ; (3) the proximal infero-marginalia are very little 

 differentiated and alternate with the adambulacralia. 



Measurements. — 218c gives R : r :: 36mm.: 4mm. Width of arm at base is 

 4 - 2 mm. The variation in size can be judged from the following measurements 

 of the width of the arm at the base: D. 93, 6 mm; D. 24c, 5 mm.; D. 255, 

 3*2 mm. 



Horizon and Locality. — Middle Ordovician (Llandeilo) of the Dow Hills, and 

 Upper Ordovician (Ashgillian) of Thraive Glen, Girvan, Ayrshire, Scotland. 



Regeneration of Lost Paris (Plate XII, fig. 5). — A cast taken from D. 110c 

 shows that the arm broke away about 8 mm. from the base and that regeneration 

 subsequently took place. The new portion of the arm is, as one would expect in 

 the earlier stages of growth, not so stout as the original lost part. The point is 

 interesting because marked regeneration has not been previously noted in Palaeozoic 

 Asteroidea. Schuchert states in respect to this (85, p. 37) : "Among living star- 

 fishes it is common to regrow arms that have been lost through accidental causes. 

 From the base of the severed ray a new growing tip is established, forming a 

 juvenile arm that gradually grows to full size and assumes mature characteristics. 

 Schondorf (62 pp. 96, 97) states that this habit has been pronounced since the 

 Jurassic, but that he has failed to find marked regeneration in Palaeozoic asterids. 

 He did, however, note partial replacement of minor losses among the Devonic 

 species. Stiirtz, who has handled more Palaeozoic asterids than any other 

 palaeontologist, also has not noted a single case of marked regeneration. The 

 same is true for the 400 Deoonaster eucharis found in a limited area of the Middle 

 Devonic of New York. Clarke, in describing this find (1912, pp. 44, 45), however, 

 does note a few specimens which show the existence of only four instead of the 

 normal five arms. These are the only examples of four-rayed Palaeozoic starfishes 

 so far recorded. 



" The writer has also been unable to find a single case of regeneration, but in the 

 Middle Ordovicic cryptozonian Urasterella ulrichi he describes a specimen with two 

 normally developed rays and three short stumps. All of the arms are normal for 

 the species, except for the length of three rays and their terminations, which are 

 blunt (see pi. xxix, fig. 1). It seems to him that this occurrence is not due to the 

 accident of fossilisation or weathering, but is an actual case of loss in life with 

 subsequent healing of the wounds, but without regeneration of the lost parts. 



