some Irish Sponges. 237 



small acantliostyli have a slightly curved shaft, which is 

 covered with small recurved spines along its whole length. 

 These spicules are about 0"125-0-15 mm. in length by 0"005- 

 0-008 mm. (2) The dermal spicules are strongyla, which 

 are straight and polytylote. They measure 0'35-0*5 mm. in 

 length by 0-006-0-008 mm. (3) The isochelaj arcuatee have 

 a strongly curved shaft which is very broad in front view. 

 They are 0-035-0'04 mm. in length. 



This species was dredged off the west and south-west 

 coasts of Ireland at depths of 388 and 468 fathoms. 



Hymedesmia spinosa, sp. n. 



The sponge is growing in a very thin encrustation on coral. 



The main skeleton consists of acanthostyli which are 

 placed very close together and are set vertically with their 

 lieads on the substratum. The dermal spicules are in 

 bundles which lie more or less horizontally to the surface. 



Spicules. — (1) The acanthostyli measure from 0*09 to 

 0*22 mm. in length, with a maximum diameter of 0*013 mm. 

 above the head. They cannot be separated into two groups. 

 The shaft is straight or very slightly curved. The head is 

 fairly well marked and is thickly covered with long, stout, 

 blunt spines ; the remainder of the shaft is set with recurved 

 spines. The longer spicules are more sparingly spined along 

 the shaft than are the shorter ones, and the spines are smaller. 

 (2) The dermal spicules are straight, slightly fusiform 

 tornota, measuring 0"18-0"26 mm. by 0*005 mm. (3) The 

 isochelse arcuatge are very numerous. They have a thick, 

 usually very strongly curved shaft, with short teeth. They 

 measure 0'03-0'038 mm. in length. The species is nearly 

 allied to Hymedesmia prociimhens^ Lundbeck. 

 . The sponge was dredged at two stations off the south-west 

 coast of Ireland at depths varying from 500 to 728 fathoms. 



Hymedesmia hibernica, sp. n. 



The sponge forms a thin encrustation on two specimens of 

 Caryophyllia clavus. 



The main skeleton consists of acanthostyli which stand 

 vertically with their heads on the substratum. The slender 

 dermal spicules are united into bundles which are placed 

 more or less vertically in the sponge ; they bend round 

 beneath the dermis and are continued as fibres running 

 parallel to the surface. 



Spicules. — (1) The acanthostyli fall into two groups ; the 

 longer measure from 0'25 to 0*325 mm. in length by 0*008 mm. 



