PLATE XVII. 



Page 

 rig. 1. Bolosponjia glolata, Hinde. Natural size. From the Upper Chalk at Flam- 

 borough, Yorkshire 74 



]''ig. 1 a. The same. Vertical section of another specimen from the same locality. The 

 dotted portions indicate the spicular structure, and the interspaces represent the 

 wide channels and loculi of the interior of the sponge. Natural size. 

 Fig. 1 b. The same. Portion of 1 a, enlarged thirty-two times, showing in the lighter 

 portions traces of the spicular structure. The spicules have been replaced by 

 crystalline calcite and silica, and are only recognizable where they were not in 

 close contact with each other originally. The square below the figure indicates 

 its natural size. Drawn from a transparent section by means of the camera 

 lucida. 

 Fig. 2. Bolospongia constricta, Hinde. Natural size. From the Upper Chalk at Flam- 

 borough 74 



The same. A transverse section of the same specimen. Natural size. 

 Thecosiphonia nobilis, Rcem. lu the lower portion of the specimen traces of the 

 smooth dermal layer are shown. Natural size. From the Upper Chalk of 

 Wiltshire. The specimen figured belongs to the Jermyn-Street Museum . . 75 

 The same. Portion of the interior spicular skeleton, enlarged thirty-two times, as 



shown on the upper surface of the same specimen. 

 Thecosiphonia turbinate, Hinde. A silicified specimen, from the Upper ChaUc at 

 Stockton, Wiltshire, showing some of the canals extending down the upper 

 surface, and traces of the corrugated dermal layer beneath. Natural size . . 75 

 Fig. 5. Thamnosporiffia glabra, Hinde. A single branching stem, forming part of a large 

 bushy mass. Natural size. Inclosed in the cavity of a flint from the Upper 



Chalk at Berkhampton 79 



Fig. 5 a. The same. Portion of the interior spicular structure immediately beneath the 



dermal layer, showing the tuberculated spicules. Enlarged sixty-four times. 

 Fig. 5 b. The same. Portion of the dermal layer of fig. 5, enlarged thirty-two times. The 

 dark figures represent the hollow moulds of the larger spicules of the dermal 

 layer. The two lighter figures below represent the spicules themselves. The 

 entire dermal layer is formed of similar spicules ; but, as a rule, only the larger 

 forms can be distinguished. 

 The same. Portion of the dermal layer of a specimen, enlarged thirty-two times, 

 showing slightly elevated spaces with groups of circular pores. From Upper- 

 Chalk detritus at Budleigh Salterton, Devonshire. Presented to the Museum 

 by Mr. H. J. Carter, F.R.S. 



Jifr. o c. 



