KONGL. SV. VET. AKADKMIENS HANDL. BAND. |9. N:0 7. 85 



These are the leading features that charaeterise the skeleton of the Pourtalesiaflie. 

 They eouibine to make them eminently Neonoinous, and different from the oldest of 

 these, the Ecliinoneida). With the Cassidulida^, of Oolitic origin, 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 Spatangidaj, the Prymnodesmians, 

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

 oesophageal opening, the heteronomy of the interradium 1, the sternum and epister- 

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

 the Spatangida3 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 mouth 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 I and Sal being i-aised above the ventral plane and out of contact 

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

 this disposition as, also, by tlie 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 degree realised, almost to the disappearance of an otlierwise 

 universal obliquity indicating the existence of an axis (uo^ l\ — 1; by the annular dis- 

 position of the intcrradia 1 and 4, forming a closed ring all around the middle of the 

 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- 

 siada;, 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 well as those in which they stand alone, demand the creation for 

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

 Spatangidas: the roURTALESiADiE. 



Geographically the Pourtalesiaduj are distrijjuted over the whole of the oceans. 

 P. Jeff'reysi seems to belong to the Norwegian Sea, having been found by the Porcu- 

 pine halfway between Fajroe and Shetland, and by the naturalists of the Voringen 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 pourtales and by the Blake in the Straits of Florida. 

 P. phiale was tirst found by the Porcupine in the llockall Channel, then again in the 

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

 hispida, P. ceratopyga 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 deptii 2900 metres; P. hispida, two habitats m. d. 3300 m.; P. carinata 



