MEMBRANIPO11A MONOSTAC1IYS. 133 



colony. The two erect spines at the top of the cell are 

 1'ivqiiriitly associated with it, though very commonly 

 absent. The lateral spines seem to be rarely developed. 

 In a beautiful variety from Roach River, the branches 

 are mostly uniserial, and the margin of the cells is clothed 

 with about sixteen delicate spines, which bend inwards 

 over the aperture. I have a similar variety from Tor- 

 quay. Specimens of this form bear a curious general 

 resemblance to Hlppothoa dentata, Busk, a Crag species. 



In the variety (fossaria), which occurs in brackish waters, 

 the aperture is much elongated and occupies the whole, 

 or nearly the whole, of the front of the cell. The pro- 

 duced pedunculate portion at the base has disappeared, 

 and with it most of the characteristic fades of the species. 

 There is a single stout conical spine at the lower extremity 

 of the aperture. The cells seem to be composed of less- 

 solid material than in the normal form; and, from the 

 nature of the base over which it spreads, the zoarium 

 assumes a peculiar habit. 



HABITAT. On rocks between tide-marks ; on shells and 

 stones, chiefly at the mouths of rivers ; and on the stems 

 of water plants in brackish ditches. 



LOCALITIES. Mouth of the river Deben, on the Suffolk 

 coast, abundant (Busk) : Roach River (J. G. Jeffreys) : 

 Torquay, on stone between tide-marks; Ilfracombe, on 

 the Capstone rocks (T. H.) : Hastings (Miss Jelly). 



Far. a. Yarmouth, in ditches of brackish water, about a 

 mile from the sea, on stems of aquatic plants (Mr. 

 AYigham) . 



GEOGRAPHICAL DISTRIBUTION. " I have a specimen very 

 like this species, from St. Vincent, one of the Cape de 

 Verde Islands" (Busk): "minus expressam hanc formam 

 ad Bahusiam vidi " (Smitt) . 



RANGE IN TIME. Red Crag, on shells (Mactra, Mya, 



