154 PALEONTOLOGY 



5. Tornoceras simplex is said to attain a diameter 

 of 75 mm., but it is not often that specimens are found 

 much larger than that figured, the size and proportions 

 of which stated in the method already explained are 



The umbilicus is either entirely closed, or too small to be 

 measured accurately. 



The body-chamber extends through about half a 

 whorl (it may be longer). The cast is nearly smooth^ 

 but shows growth-lines (radial lines) whose course is 

 similar to that of Manticoceras. The suture-line, how- 

 ever, is quite different : the external lobe is narrow and 

 undivided ; on each side of it is a rounded external 

 saddle, a rounded lateral lobe and a rounded lateral 

 saddle (Fig. 47, c). It is the lobe that comes in the 

 middle of the lateral area, so that the contrast with 

 Manticoceras is striking. 



6. Gastrioceras carbonarium (Fig. 44) occurs in 

 some abundance in the marine bands which form the 

 "roofs" of certain coal-seams in the Lower Coal Measures 

 of Lancashire and Yorkshire. Specimens have been 

 found as much as 160 mm. in diameter, but a more usual 

 size is about 30 mm. and one of these small specimens 

 gives the following proportions (the query to the last 

 item denotes difficulty of measurements owing to the 

 umbilicus being filled with tough shaley matrix) : 



30 : 45'5> 6o > 4 ? 

 The inner area falls very steeply from the umbilical 



