246 A MONOGRAPH OF THE 



long shaft projected from the semicircular base of the fork. 

 In the spiculum of Il.forcipis this shaft is not present. 

 The structure of the forcepiform spiculum is very interest- 

 ing ; the semicircular base is much the stouter portion of 

 it, and each limb gradually attenuates to its distal termi- 

 nation, ending in an extremely fine point ; sometimes the 

 limbs are equal in length, but more frequently one is con- 

 siderably longer than the other. In some cases, the two 

 run parallel to each other, but more frequently their distal 

 extremities approach until their apices are in contact, or 

 very nearly so. The minute spines are numerous ; they 

 extend over all parts of the spiculum, and the points of 

 nearly all of them are inclined backward towards the semi- 

 circular base of the spiculum. 



The large bi- and tridentate equi-anchorate retentive 

 spicula are stout, and exceedingly well produced ; the smaller 

 series of bidentate ones are very minute, and the same ob- 

 servation applies to the bihamate spicula. For the distinct 

 exhibition of the spination of the forcepiform spicula and 

 the minute anchorate and bihamate ones, a linear power of 

 600 or 700 is required. 



12. Halichondria simplex, Boiverbank. 



Sponge. Parasitical, coating Zoophytes or Fuci. Surface 

 uneven, rugged. Oscula simple, dispersed. Pores in- 

 conspicuous. Dermal membrane profusely spiculous. 

 Spicula same as those of the skeleton, dispersed, and 

 frequently indistinctly fasciculated. Skeleton. Irregu- 

 lar and diffuse in structure ; rete, spicula few in num- 

 ber, occasionally multispiculous ; spicula acuate, long, 

 and stout, frequently flexuous. Interstitial membrane 

 rarely spiculous ; spicula same as those of the 

 skeleton. 



Colour. Light gray. 



Habitat. Shetland, Mr. C. W. Peach. 



Examined. In the dried state. 



