SPONGES. 65 



in waters which are probably very rarely reduced, even during the month of January, 

 to 55°, and perhaps for the best qualities not below 60° F. 



Marketable sponges are found in the Mediterranean on the coast between Ceuta on 

 the African side, and Trieste on the Adriatic. None are found in the Black Sea, 

 on the coasts of Italy, France, or Spain, or the Islands of Corsica, Sardinia, the 

 Balearic Islands, or even Sicily. The species do not usually appear in water deeper 

 than thirty fathoms. They are gathered by means of hooks on long poles, or direetly 

 by the hands of divers, or, as in the case of some of the coarser kinds, dragged up 

 roughly by dredges. When secured they are exposed to the air for a limited time, 

 either in the boats or on shore, and then throwh in heaps into the water again in pens 

 or tanks built for the purpose. Decay takes place with great rapidity, and when fully 

 decayed they are fished up again, and the animal matter beaten, squeezed, or washed 

 out, leaving the cleaned skeleton ready for the market. In this condition, after being 

 dried and sorted, they are sold to the dealers who have them trimmed, re-sorted, and 

 put up in bales or on strings ready for exportation. There are many modifications of 

 these processes in different places, but in a general way these are the essential steps 

 through which the sponge passes before it is considered suitable for domestic purposes. 

 Bleaching-powders or acids are sometimes used to lighten the color, but these, unless 

 very delicately handled, injure the durability of the fibres. 



The first fossils which undoubtedly belong to this group occur in the carboniferous 

 rocks. Carter having described a Dysidea from this period, but masses supposed to 

 belong to the Sponginse have been found in much older rocks. 



Sttb-Oedeb II. — Aplysin^. 



These sponges have a skeleton composed of fibres which are hollow or filled with a 

 soft, friable core, and there are no foreign materials introduced from the exterior. 

 The fibres are not as elastic as those of the Sponginse and generally are much larger 

 and coarser. The sponges are dendritic or grow in sheets, often of considerable size. 

 The skeletons are more open in structure than in the last sub-order, and frequently the 

 fibres have a fan-like arrangement. No fossils are known. 



Okdee IV. — KERATO-SILICOIDEA. 



As the name implies, this division fonns a transition between the horny and the 

 silicious sponges. The skeletons are formed of solid keratose fibres and silicious 

 spicules. 



Sub-Oedee. I. — Rhaphidonemata. 



In this group the spicules are of one kind only, usually with pointed ends, and are 

 loosely arranged in the vertical and horizontal fibres of the skeleton, and covered by 

 the keratode, though often but slightly bound together. The keratode is light-colored 

 or transparent. This division is represented on our eastern coast by the well-known 

 Dead-man's-finger Sponge, Chalinula ocidata. This is a bushy form, common on piles 

 or rocks, especially in tide-ways where there is a considerable current of clear water. 

 It sometimes grows to a height of two feet. The cloacal openings are small and 

 irregularly scattered over the surface of the branches, while the ^ores are imperceptible 

 to the naked eye. The color is brown, sometimes softened by a warm undertone of 



VOL. I.— 5 



