KONGL. SV. VIOT. AKADEMIENS IIANDL. BAND. |9. N:0 7. 85 



These ai"c the leacliiig features that cliaracterisc the skcluton of tlic Pourtalesiadas. 

 They combine to make them eminently Neoiioinous, and diflercnt from the oldest of 

 these, the Echinoneida;. With the Cassidulida3, of Oolitic origii), they have in com- 

 mon the caudal prolongation, the structure of the proctal part, and, in some degree, 

 the simple form of the pedicels. With the higher Spatangidaa, the Prymnodesmians, 

 they share in the abdominal lengthening of the body, the forward position of tlie 

 oesophageal opening, the heteronomy of the interradiura 1, the steriium and epister- 

 num, the fasciola, the form of the spines. They fail to attain the high standard of 

 the Spatangidai by the frequent abortion of the organs of vision, by the pedicels uni- 

 formly simple, not specialised into tactual, prehensile, branchial organs distributed on 

 differently modified parts of the ambulacra. The line of modification followed by their 

 special development goes in another direction, indicated by the cylindroid form of the 

 body, the forward position and the degradation of the calycinal system, the incipient 

 feature of a rudimentary moutli and buccal cavity, with the oesophageal opening and 

 the peristome vertical, by the peristomal part of the frontal ambulacrum and the in- 

 terradials 2 b 1 and o a 1 being raised above the ventral plaile and out of contact 

 with the ground; by the contrast between the dorsal and ventral segment heightened by 

 this disposition as, also, by the entire set of spherids and the larger pedicels being station- 

 ed on the sub-labial area; by the symmetrical disposition of the parts on either side 

 thus being to a certain degTce realised, almost to the disappearance of an othei'wise 

 universal obliquity indicating the existence of an axis «w, IV — 1; by the annular dis- 

 position of the interradia 1 and 4, forming a closed ring all around the middleofthe 

 body, and, as a consequence, the dismemberment and backward transposition of the 

 fettered hind-limbs, the ambulacra I and V. These are characters in the Pourtale- 

 siadte, pointing, though remotely, towards animal forms of another and higher type, 

 animals of annulose differentiation. The sum of these features, those shared with 

 other groups as wcll as those in which they stånd alone, demand the creation for 

 them of a distinct family, systematically equivalent to that of the Cassidulida3 and the 

 Spatangidaj: the POURTALESiADiE. 



Geographically the Pourtalesiadaj are distributed över the whole of the oceans. 

 P. Jeffrej^si seems to belong to the Norwegian Sea, having been found by the Porcu- 

 pine halfway between FaBröe and Shetland, and by the naturalists of the Vöringen at 

 Lat. 63° 6' N., long. 1° 20' W.; Lat. 63° 10' N., long. 5° E.; Lat. 67° 20' N., long. 9° 

 E. P. miranda was dredged by de pourtalÉs and by the Blake in the Straits of Florida. 

 P. phiale was first found by the Porcupine in the Rockall Channel, then again in the 

 Antarctic Sea, by the Challenger. P. laguncula and P. rosea are from the Pacific; P. 

 hispida, P. cei^atopyga and P. carinata Antarctic, the two last reaching the coast of 

 Chile. Echinocrepis cuneata and Spatagocystis Challengeri are Antarctic. 



Bathymetrically the Pourtalesiada^ have been found at depths from 442 to 5300 

 metres, the average depth being 2900 m. Seven species were met with from this point 

 and downwards, in Globigerina ooze, grey ooze, and red clay: Pourtalesia phiale, two 

 habitats, mean depth 2900 metres; P. hispida, two habitats m. d. 3300 m.; P. carinata 



