74 C. E. Beecher — Development of Shell in Tornoeeras. 



turn, there is a well-developed sinus over the siphuncle, forming 

 a rounded ventral lobe, and a broad lateral saddle, with a cor- 

 responding, though less prominent, dorsal saddle. The third 

 and. following septa present more and more sharply angular 

 ventral lobes, until finally it is further extended by a siphonal 

 fissure in post-nepionic stages. The lateral saddle is nut so 

 strongly curved from the fourth to the seventh suture which 

 is quite flat, but in the eighth, a slight retral bend is observable. 

 This evidently marks the inception of the lateral lobe. The 

 septum is now divided into the leading members characteristic 

 of the group, viz : a ventral lobe and saddle, a lateral lobe and 

 saddle, a dorsal saddle and an annular lobe, although the two 

 latter are less strongly marked than the others. Further 

 growth merely serves to emphasize these features, until the 

 nealogic stadium, when the ventral lobe is extended by the 

 siphonal fissure, and a minute cone appears at the bottom of 

 the annular lobe. 



Several specimens of the protoconch give evidence of the 

 presence of the siphonal ccecum, and show that it was probably 

 closely appressed to the ventral wall. Figure 3 illustrates the 

 ovoid, marking on the interior of the shell, enclosing two 

 diverging lines which apparently represent the appressed por- 

 tion of the true ccecum, while the outer curved lines limit the 

 shelly deposit of attachment. The relative diameter of the 

 siphon at the first and for a number of succeeding chambers is 

 much greater than in the mature shell (figures 1, 6, 13). From 

 the beginning, it is situated close to the abdominal wall, and is 

 nearly invariable in its character. 



The embryonic shell is very thin, and almost smooth in its 

 earlier portions ; then fine revolving lines of granules appear, 

 which become progressively more pronounced and arranged in 

 transverse rows, between which the earliest of the concentric 

 strise are developed. With the increase in the strength of the 

 stride, the granules disappear, and are obsolescent before the 

 protoconch is completed (figure 7). The striae are sharp, 

 elevated, and straight, forming a conspicuous feature of the 

 ornamentation, until in the third or fourth whorl, when they 

 become subdued, and finally are replaced by the fine inconspic- 

 uous and often fasciculate lines of growth which are present 

 in the adult shell. .No indication of a funnel is shown up to 

 the completion of the first whorl (figure 10), as the striae 

 continue straight across the ventrum, but in the second (figure 

 11), the pronounced sinus in the striae shows that the funnel 

 had developed or, at least, had become of functional importance. 



A. comparison of the figures of T. retrorsum, v. B., var. 

 typum, Sand., as illustrated by Branco (loc. cit. pi. v. fig. vii), 

 with the present species shows that the former presents a more 



