On a new Species of Acis. 381 



species of Atya which issued from it. It is easy to verify upon 

 the spot the exactness of the views expressed in this note. 

 Those who do not accept them may always regard the two modi- 

 fications described above as distinct species of Ortmannia *. 



XLIV. — Notes on a new Species of Acis. By W. D. 

 Hendekson, M.A., B.Sc, Zoological Laboratory, the 

 University, Aberdeen. 



While working along with Prof. J. Arthur Thomson over a 

 collection of Indian-Ocean Alcyonarians I recognized the new 

 species here described. It was included in a collection made 

 by Prof. W. A. Herdman in Ceylon. 



The colony is large and fan-shaped, rising to a height of 

 149 mm. and having a maximum width of 167 mm. 



From a conical base, which has a flat spreading margin and 

 is attached to a mass of worm-tubes, the short main stem 

 arises. At a distance of 14 mm. from its origin, where it 

 has a diameter of 3*5 mm., it divides into two principal 

 branches. 



The branching is for the most part confined to one plane, 

 but several of the smaller branches and twigs arise at right 

 angles to the principal plane of branching. The branching 

 is very profuse and at several points shows anastomosis of 

 the branches, but this is by no means common. The branches 

 are cylindrical, but there are traces of slight flattening in the 

 plane of branching. The twigs arise usually at right angles 

 to the branches, and their tips as well as those of the branches 

 are slightly clavate. 



The polyps are small and are scattered over the whole 

 surface of the stem and branches. In no place can it be said 

 that they are confined to three surfaces, nor can any attempt 

 at lateral arrangement be seen. The verrucas are very small 

 and the polyps can be completely retracted within them. 

 The edges of the verruca? show a variable number of spines 

 which project above the slightly conical operculum formed by 

 the tentacular spicules when the polyps are withdrawn. 



The superficial ccenenchyma of the stem and the branches 

 presents a striking appearance, due to the arrangement of the 

 large flat whitish spicules and to their being outlined against 

 the darker ground-colour of the stem and branches. 



The spicules of the general ccenenchyma are flat and multi- 

 tuberculate, varying very much in size and shape. The 



* M. Ortmann regards Atya bisulcata, Spence Bate, as an Ortmannia 

 (Atyoida), although the examples studied by the English author had the 

 true Atyan chelae ; I may add that M. Ortmann does not appear to have 

 observed the curious variations of this species. 



