64 University of Texas Bulletin 



secondary saddle and a pointed secondary lobe; the siphonal lobe is 

 deep and much narrower at the upper end than below the middle, at 

 the height of the secondary lobes. It is relatively much broader and 

 shorter than in the adult suture. The first lateral lobe is very broad and 

 divided in two branches by a small secondary saddle ; both branches, 

 as well as the secondary saddle, are rounded. The second lat- 

 eral lobe is about half as broad as the first one, rounded at the bottom 

 and much narrower at the upper part than below. The first and second 

 auxiliary lobes are much smaller and less deep than the two lateral 

 ones. The saddles are all entire and rounded at the top. The external 

 saddle is not very high and bends slightly toward the sipho ; the first 

 lateral saddle is higher than the external and constricted above the 

 base ; the second lateral saddle is similar to the first, but a little lower ; 

 the first auxiliary is much lower than the preceding one; also much 

 narrower and not constricted; the second auxiliary, which lies on 

 the umbilical wall, is an insignificant saddle. 



From the point where the median furrow on the venter develops, 

 the suture begins to change materially. The secondary saddle in the 

 first lateral lobe bulges slightly on its side nearest to the siphonal re- 

 gion and becomes asymmetrical; at the same time the number of 

 auxiliary lobes and saddles on the flank near the umbilical region 

 increases rapidly. Afterwards, the exterior portion of the secondary 

 saddle in the first lateral grows much quicker than the interior one; 

 at about the fourth part of a whorl from the point where the median 

 furrow begins, the aforesaid secondary saddle becomes still further 

 subdivided. Its inner bulge has developed into an independent sec- 

 ondary saddle and now becomes indented and divided in two equal 

 parts, while the outer portion of the original secondary saddle has 

 grown so far that it could almost be considered as an independent 

 lateral saddle ; but its development shows that it has to be regarded as 

 a secondary one, belonging to the first lateral lohe. Here the suture 

 has reached its adult stage and consists now of eight saddles and 

 eight lateral and auxiliary lobes between the umbilical border and 

 the sipho. 



This ulitimate stage of the suture has the following character (pi. 

 I, fig. 24-25). The siphonal lobe is deep and very narrow, and oc- 

 cupies about the width of the median furrow on the venter. It is 



