PORIFERA. II. 



215 



there is generally found, in the middle of the inner side of the axial part, a little round notch, often 

 bounded on either side by a small spur; on the fourth arc, on the other hand, the arc that is the 

 original axis, only a spur or a few spurs are found. The sphasrancorse may be somewhat varying in 

 appearance; they may especially be more or less highly arcuate, so that the ellipse may be longer or 

 shorter; the shorter and more highly arcuate ones are upon the whole more robust, and have broader 

 arcs than the longer and more slender ones. These variations of the sphserancorse are generally found 

 in different individuals, while in one individual the variation is most frequently slight. Further some 

 more or less monstrously or irregularly developed forms are seen; thus the ancorse may be somewhat 

 twisted, and the consequence then is that the teeth do not meet; in this case they either coalesce in 

 an oblique way, or are left free. Sometimes the teeth do not reach their full length, so that the coa- 

 lescing remains incomplete, or does not take place at all, while in other respects the ancorse are fully 

 developed. 



The description of the construction and mode of growth of the sphserancorse given here is quite 

 agreeing with Levin sen's observations, with the only exception of a few points. Levi us en's opinion 

 is that two independent forms of sphserancorse are found, smooth ones and striated ones; but the smooth 

 ancorse, as has been advanced here, are developmental stages of the striated ones, only they have not 

 yet got the striated lateral brims, which grow forth as the last feature, and may be followed in their 

 growing to greater breadth, so that we get a continuous series from the first stage to the finished 

 sphserancorse (PI. XX, fig. ic — k). The reason why Levinsen has supposed two independent forms to 

 exist, is that he regards the forms with free, not coalesced, but otherwise fully developed, striated teeth 

 mentioned above as the developmental forms of the striated ancora. According to what has been 

 stated above, there can be no doubt, however, that these ancorse are quite complete and their growth 

 finished; they have only a little shorter teeth than the other sphserancorse, which leads to the fact that 

 the teeth do not coalesce; they are. accordingly, to be regarded as monstrous forms. Levinsen is 

 also surprised that he finds only very few of the developmental forms of the striated ancora and no 

 young ones, as he refers all the younger developmental forms to the smooth ancora ; these latter develop- 

 mental forms are rather frequent, although the smooth ancora is far less frequent than the striated one; 

 this latter fact is a matter of course, as the smooth ancora is a developmental form. Levinsen, it 

 must be added, says himself that it is the finding of the striated ancora with not-adjoining teeth, which 

 causes him to suppose two forms, while he should otherwise have been inclined to regard the smooth 

 ancora as a developmental form of the striated one. 



The length of the sphserancorse varies from 0-054 — o-o68 m ™, and the breadth, measured across 

 two opposite arcs, varies from 0-024 — o-038 mm . 2. The ancorse of the large form are of the 

 common structure; they have a slightly curved shaft and three lanceolate teeth at each end, and a 

 narrow ala of the same length as the teeth. The ancorse are somewhat varying in size, the length 

 from 0-047 — o-o75 mm ; the variation, however, is not so large in one individual, as instances may be 

 given 0-047 — o-o6i mm , and 0-057— 0-075™™. The breadth is ca. 0-017 — o-02i mi ". A few developmental 

 forms occurred; these, as already mentioned, may easily be distinguished from the developmental forms 

 of the sphserancora, as their beginning teeth at an early stage become high and narrow, i. e. develop 

 a falx, while such is not the case with the sphserancorse. 3. The small ancorse are of a similar 



