the Crinoidese and the Echinodermata. 287 



approaches that of a Goniaster ; and if the ovarial pores in Acti- 

 nocrinus are situated at the base of the rays, as is generally be- 

 lieved, then the resemblance becomes more complete ; the dif- 

 ference in this respect being that in Goniaster the ovarian pores 

 are marginal and situated between the rays, and in Actinocrinus 

 at the points from whence the rays emanate. The Actinocrinus 

 section also closely resembles in outline an impregnated Apio- 

 crinus, making the connecting links still more perfect. 



In the American Ayaricocrinus of Dr. Troost, the ovarial ducts 

 are clearly seen at the base of the rays. This newly discovered 

 genus, forming as it does a connecting link between the genera 

 Actinocrinus and Amphoracrinus, again shows the gradations by 

 analogy that exist between the different genera in the whole 

 group. 



Passing from the Encrinites proper, another very singular 

 extinct family presents itself to our notice, of which we have no 

 exact type in the living creation, namely the v Blastoidea, esta- 

 blished by Say. This family contains but one genus, named Pen- 

 tremites. The genus may be defined thus : — Perisomic plates 

 so united and fitted to each other as to completely inclose the 

 digestive organs and generative system ; the mouth and ovarial 

 pores placed on and around the apex ; branchiae arranged in five 

 ambulacral rows; column cylindrical, perforated in the centre 

 and composed of numerous articulating joints; arms none. 



This remarkable genus bears so little affinity to any other yet 

 discovered, excepting Dr. Troost's recent discovery of the Oliva- 

 nites, to which it is allied, that it cannot with propriety be re- 

 ferred to any natural family hitherto instituted, for to those 

 which most nearly approach it, it is but remotely and obscurely 

 allied. Its columnar attachment seems to connect it with the 

 true Crinoids, but the absence of projecting rays altogether ex- 

 cludes it from that group ; while the body in which are situated 

 the ambulacral cilia, circularly placed openings and the central 

 generally angulated one, proves its affinity to the Echinidce, but 

 the columnar support and attachment prove that it cannot be 

 properly grouped with them. 



Considerable analogy also exists between some species of Pen- 

 tremites, the P. inflatus and P. pentangularis for example, and 

 the Star-fishes. Likewise, if the internal sac of a small Goni- 

 aster be filled or inflated to turgidity, the body assumes a conoid 

 form, and then the general resemblance becomes strikingly ob- 

 vious, while the ovarial apertures bear considerable analogy to 

 each other. The Pentremites astraformis even more nearly ap- 

 proaches the Goniaster Templetoni (Thompson) than the P. in- 

 flatus or P. pentangularis . It also presents on its ventral surface 

 some characters common to both Asterias and Ophiura. The 



