308 Mr. F. A. Bather 07i Shell-groicth 



region of the shell-wall was rapid ; the septal and sheath- 

 niemhranes were numerous or only partially calcified, and 

 their edges appeared as lines of growth on the shell-wall ; for 

 this branch Fischer has kept the name Chondrophora (4), 

 meaning by ^j^ovS/ao? not cartilage, but chitin ; among its 

 earliest examples are Coccoteutlns and Geoteuthis of the Solen- 

 hofen slate. In the other branch the shell grew more slowly 

 and the membranes were still fully calcified ; since it is both 

 opposite and parallel to Chondrophora, I propose for it the 

 corresponding name Osteophora'^, which is no more mis- 

 leading and has the merit of being Greek. This branch con- 

 sists of the Phragmophora and Hefiophora of Fischer ; but 

 these names merely describe stages in one series, not diver- 

 gent groups. Not till the Tertiary era did phylogenetic 

 retrogression influence this branch. Then the septa gradually 

 became more closely set, and their membranes, as well as 

 those of the sheath, less calcified. Naturally the extreme 

 form thus produced, viz. Sepia, simulates the earlier Chondro- 

 phora ; but it is still well calcified, and its genetic history is 

 diff'erent. The evidence of fossils emphasizes the distinction : 

 in Osteopjhora the part preserved is the calcified portion of the 

 sheath (guard and mucro) ; in Chondrophora we only find 

 the semicalcified chitinous laminae. Sepia is not yet known 

 in the Solenhofen slate, though the ghost of this ancient 

 belief still shrieks to be laid. Fit places are found in this 

 scheme for Spirula and Loligo, as I show elsewhere (14). 



Since, however, the sepion has been chosen as battle- 

 ground, it is as well to summarize here conclusions respecting 

 it. Secretion of chitin is rapid in proportion to growth ; 

 more membranes are deposited than can be calcified ; some 

 of these remain free- stretched, the others are seen in the 

 septa. At its antero-dorsal margin each membrane is 

 rapidly covered by a fresh one ; the edges, which thus 

 remain uncalcified, form the middle plate ; this was repre- 

 sented in the Belemnite by an epicuticula of the phrag- 

 mocone. In the sheath-membranes, deposited by the mantle, 

 calcification takes place with more or less completeness at 

 different stages, according to the varying rapidity of secretion. 

 As it is the youngest portion of the inner shell that most 

 resembles the Belemnite-phragmocone (14), so is it that part 

 of the outer plate covering the young portion which most 



* Kefersteiu, iu Bronn's ' Klasseu u. Ordnungen,' thus distinguislied 

 recent forms, and spoke of Devajyoda cakiphora (p. 1438) ; but he did not 

 recognize their true affinities. As my grouping is not quite the same as 

 his, 1 seize the opportunity of rejecting his barbarous epithet. 



