DlCTYOSPONGID^E. 



383 



without interruption, and probably were originally continuous to the base of 

 the sponge. The upper or outer portions of these spicular bundles contain 

 numerous small cylindrical rods which terminate in a two-pronged anchor, 

 each barb or prong tapering 

 backward toward the aperture 

 into a slender rod ending in a 

 point. The head of the anchor 

 is considerably inflated on the 

 smooth surfaces and its apex or 

 point is blunt. The size of the 

 anchors varies somewhat, as 

 shown in the accompanying fig- 

 ure, both enlargements to the 

 same degree. These anchorate 

 spicules are scattered, often 

 abundantly, throughout the en- 

 tire length of the lateralia and 

 could have had nothing to do 

 with the fixation or anchoring 

 of the sponge. 



Together with the anchorate spicules or just above them and on the 

 outermost layer of the bundles, is a series of parallel twigs or denies which 

 have been described as somewhat flattened rods expanded alternately first on 

 one lateral margin and then on the other, into j 

 elongate triangular surfaces whose outer or mar- 

 ginal angle is acute and continued a short dis- 

 tance backward into a very slender rod-like exten- 

 sion. Between this and the edge of the spicules 

 the margin of the triangle is gently incurved. 

 The intervals between the triangular expansions 

 vary somewhat, and the spicules themselves are 

 generally more slender than the rods of the gas- 

 tral surface, though they are seen to be of con- 

 siderable length. One specimen, which happens 

 to be the original of UphanUrnia Dawsoni, 

 Whitfield, is so broken that a portion of these vertical bundles remains 

 on the interior or gastral cast and the rest or outer portion on the 

 enclosing rock. The former of these fragments is figured by Whitfield 



Fiours 89. Physospongia Daw$oni. 

 ules. X400. (J. M. C.) 



The head! of two anchorate aplo- 



FIOURE 40. P?iysospongia Dawsoni. A 

 group of spicules. The stauractln In the clrcla 

 Is enlarged 30 diameters ; the others 250 di- 

 ameters. (J. M. C> 



