30 C. F. JENKIN. 



ACHRAMORPHA. 



Staurorrhaphids in whicli tlie elongated flagellated chambers are arranged radially 

 round the central gastral cavity ; they are covered over by a dermal cortex, composed 

 principally of triradiate spicules, and without longitudinally disposed oxea. The 

 tubar skeleton is articulate, the ifirst (and sometimes only) joint being formed of 

 chiactines. 



The definition of this new genus in the family Staurorrhapliidae corresponds to 

 that of Grantia in the Grantiidse, but omits the limitation introduced by Dendy, which 

 transfers all Grantise with tufts of spicules, including Grantia compressa, to the 

 family Sycettidse. This limitation appears to be artificial and unsatisfactory. 



The genus contains three species, Achramorpha nivalis* Achramorpha glacialis* 

 and Achramorpha grandinis* 



In all the species the flagellated chamber skeleton consists of the basal rays of the 

 chiactines. There is no gastral skeleton proper ; the gastral layer is supported by the 

 paired rays of the chiactines, except in the oscular tube, where there are quadriradiates 

 lying tangentially in the ordinary position, i.e., in the gastral layer, with the basal ray 

 pointing downwards. At the junction between the oscular tube and the body, the 

 quadriradiates lie at all angles intermediate between the centrifugal position and the 

 tangential position. This remarkable change in position of the quadriradiates 

 in passing from the oscular tube to the body, which is conspicuous in this 

 genus, is discussed in Part III. 



The skeleton of the dermal cortex consists of triradiates lying tangentially with 

 the basal ray, pointing more or less downwards ; there are also large projecting oxea. 

 In one species there are also projecting hair oxea, and in the other two there are 

 minute prickly hastate oxea projecting round the ostia. 



In two of the species the skeleton of the oscular edge is well difiierentiated. It 

 consists of a few rows of special quadriradiates closely and regularly packed, and 

 partially hidden in the dense fringe of oxea. In the top row these quadriradiates have 

 remarkably snub apical rays, which usually hardly penetrate through the fringe. 

 From these apical rays springs the diaphragm which closes the oscule (Figs. 100 & 102). 

 This diaphragm can be made out in some specimens, but not in others, probably owing 

 to defective preservation. 



In the third species, A. grandinis, the oscular skeleton is hardly difierentiated 

 from the body skeleton and there is no fringe. 



In all the species the flagellated chambers open one or more together into small 

 shallow excurrent chambers, which open into the gastral cavity through ports in the 

 gastral membrane. 



* Ignis, grando, nix, glades spiritus procellarum qucB faciuni verbum ems. 



