484 RECORD or science for 1886. 



movable proboscis, at the end of which a mouth-opening eventually 

 appears. After the disruption of the stolon the individualized buds 

 seem to be nourished at the expense of the yolk stored up in their ca^i- 

 ties. These cavities, which extend even to the end oftthe tentacles, 

 may be justly termed gastral cavities. 



" The liberated mother bud (B), with twenty-four tentacles, is divided 

 into two daughter forms (B^), with twelve each. These divide and give 

 rise to two different forms, B^ and B^ft. The successive multiplication 

 of the different generations is fully discussed and tabulated, and the 

 three forms are described." 



In brief. Dr. Ussow regards the Polypodmm as ''a hydroid organism, 

 with a motile ' trophosome' (B) passing through various assexual gen- 

 erations before attaining the sexual (possibly medusoid) form. The 

 planula of the latter migrates into the ovum" of the sturgeon, and 

 "gradually develops into the stolon, with primary and secondary buds." 

 (Morph. Jahrb., xii, pp. 137-153, 2 pL; J. K. M. S. (2), vi, pp. SOS- 

 SOS.) 



ECHINODERMS. 



Pehnatozoans. 



Diversify among the hlastoids. — The pelmatozoans or crinoids, although 

 comparatively rare at present, were formerly very abundant, and in the 

 palsezoic seas represented by many diverse types. Among the most 

 singular of these were the bhistoids, which have been by most au- 

 thors regarded as an order of the pelmatozoans, but recently Dr. P. 

 Herbert Carpenter has contended that the group is separable from the 

 crinoids as a class. A monograph of the group has been recently pub- 

 lished by Mr. Robert Etheridge and Dr. P. Herbert Carpenter as a 

 " catalogue of the blastoidea in the geological department of the British 

 Museum." The authors maintain that "the blastoidea constitute a re- 

 markably compact group, which is pretty clearly marked off from the 

 other pelmatozoa." They find that the perforate lancet j^late and the 

 regular limitation of the hydrospires to the radial and the inter-radial 

 plates, with their slits parallel to the ambulacra, are characters which 

 are not as yet known to occur in either the crinoidea or the cystidea. 

 Thg group thus distinguished is divided by Messrs. Etheridge and 

 Carpenter into six families, which are segregated under two orders. 



One order, the Eegulares, includes "pedunculate blastoids with a 

 symmetrical base, in which the radials and ambulacra are all equal and 

 similar." This group includes four families : (1) Pentremitidw, with three 

 genera, the chief of which is the genus so well known to American 

 I)aleontologists under the name Pentremites, and (2) Troostoblastidce, 

 a new family, with three genera, two of which have been established by 

 American naturalists; (3) Nucleohlastidw, also a new family, including 

 four genera, one of which is made the type of the subfamily Ekeacrinidce, 

 while the other three belong to a second subfamily, Schizoblastidce ; (4) 



