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Order Lithistida, Oscar Schmidt. 



In this order are comprised sponges whose skeleton is 

 built up (if spicules which are united to;:4Cther by the inter- 

 locking of the extremities of their arms to form a more 

 or less open mesh or net work. In addition to the spicules 

 composing the mesh-work of the body of the sponge, there 

 are, in most, if not all the Lithistids, other spicules, frequently 

 of quite a different form to those of the mesh, which are 

 arranged on the outer surface of the sponge and may be 

 termed surface spicules in contradistinction to the mesh or 

 body spicules. In existing sponges of this order minute 'flesh' 

 spicules are also present, but these have not been preserved in 

 the fossil examples. 



The intimate manner in which the spicules of the mesh 

 are interwo\'en together by the curiously modified extremities 

 of their arms , has enabled the sponges of this order to retain 

 in many instances their form complete in a fossil condition. 

 As remarked by Zittel (Studien p. 79) the spicules do not 

 usually fall asunder and become detached after the death of 

 the animal , and Mr. Carter has also recently stated that the 

 mesh spicules of existing Lithistids are, for the most part, so 

 locked together that even boiling in nitric acid does not cause 

 them to detach and fall asunder. (An. Mag. N. Hist. S. 5, 

 Vol. 6 p. 496). It is to this fact that the larger portion of 

 known fossil sponges belong to this order , though , if one 

 may judge from the proportion of the detached spicules of 

 Tetractinellid sponges in this Horstead flint, as well as at 

 Haldon and in Westphalia, the Tetractinellids may have been 

 equally as numerous in the same strata with the Lithistids, but 

 that owing to their skeleton being built up of disconnected 

 spicules, and the inevitable dispersion of these in nearly all 

 cases after the death of the animal, their remains have, up 

 to the present, been but little noticed. At the same time 

 that the skeleton of fossil Lithistid sponges has been very 



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