476 



ANNELIDA. 



aperture at its broad end. The internal cast of the tube has the 

 form of a series of inverted conical rings, of small width, arranged 

 in an imbricating manner. The most remarkable feature about 

 Cornulites is, however, the peculiar micro-structure of the thick 

 calcareous wall. Thin sections of the tube show that it is composed 

 principally of lenticular calcareous vesicles of considerable size (figs. 

 335, c, and 339, b), resembling in form the vesicles of a Cystiphyl- 

 loid coral. These vesicles are sometimes traversed by irregular 

 laminated bands or fibrous layers, and a similar layer seems to line 

 the interior, and cover the exterior of the tube. The inner laminated 

 layer (fig. 335, c) is sometimes of considerable thickness, and is 



Fig. 339. — Cornulites serpularius, from the 

 Wenlock Limestone, a, Tube of the natural 

 size ; b, Portion of a cross-section of the tube 

 enlarged. (Original.) 



Fig. 340. — Cornulites sp. Silurian. The 

 right-hand figure represents a cast of the 

 tube. The left-hand figure represents a 

 specimen broken below. (Original.) 



traversed by minute transverse tubuli similar to those seen in the 

 laminated calcareous tissue of some recent SerpulcE. As the tube 

 in some Serpulce. (fig. 335, b) also shows a vesicular character, the 

 microscopic structure of the tube of Cornulites is not so abnormal as 

 it has generally been supposed to be, and its Annelidan nature is, 

 on the whole, rather supported by its minute structure than dis- 

 proved. 



In the genus Ortonia (fig. 341) are included conical, slightly 

 flexuous calcareous tubes, which have a general resemblance to 

 Cornulites, but are of comparatively small size, and are cemented 

 by the whole of one surface to some foreign body such as a shell or 

 a coral. Though often found in considerable numbers, the tubes 

 are essentially solitary in habit. The tube is ringed with imbricating 



