88 TH. MORTENSEN, (Schwed. Sudpolar-Exp. 



Tnpylus excavatus Meissner. 1896. Die von Herrn Dr. Plate aus Chile heimgebrachten Seeigel. Arch. f. 



Naturgesch. I, p. 89. 



— — — 1900. Echinoiden d. Hamburger Magalh. Sammelreise, p. 14. 



Some other less important literary references are given in the two papers quoted 

 by Dr. MEISSNER. 



To the descriptions given by PHILIPPI and AGASSIZ I have to add only a few 

 remarks. 



The most important feature, the only thing, in my opinion, which justifies mak- 

 ing this species the type of a distinct genus, is found in the anterior paired ambu- 

 lacra. The petaloid condition does not continue down to the fasciole, the last 4— 5 

 ambulacral plates having only small pores; as these plates are about twice as high 

 as those above, the non-petaloid part of the ambulacrum inside the fasciole becomes 

 about one third of the whole length of the petal. This feature has not been men- 

 tioned by either Philippi or AGASSIZ, but in Philippi's figures I. a and c (PI. XI) 

 it is distinctly seen that the deepened part of the petals ends at a considerable dis- 

 tance from the fasciole, and in the fragments of Philippi's type specimen, which 

 Professor LuDWIG has most liberally lent me for examination, I find the same fea- 

 ture very distinct. This characteristic feature is thus found equally developed in 

 both sexes. (The specimens at my disposal are males.) The posterior ambulacra 

 are petaloid in their whole length. — Through the character described this species 

 is at once distinguished from the different species of Abatus, with which it otherwise 

 agrees in the prominent feature of the petals of the female being developed into 

 deep marsupia. The same character distinguishes it from Tripylaster Philippii, with 

 which it agrees in the distinctness of the latero-anal fasciole, the central position of 

 the apical system and the small spines and tubercles. — One is also reminded of 

 Agassizia by this feature of the anterior petals, and it can scarcely be doubted that 

 this latter genus is really nearly related to the Brisaster-Abatus group. (That both 

 Brisaster and Abatus pass through an vAgassiziat-stage is well worth remembering in 

 this connection.) Tr. excavatus was, indeed, referred to the genus Agassizia by 

 AGASSIZ & DESOR in their »Catalogue raisonne des Echinides*. 



As seems to be very often the case among the Irregular Echini, the right an- 

 terior side of the test projects somewhat before the left ; this holds good for all the 

 specimens in hand. 



Of the odd anterior ambulacrum PHILIPPI says that it has »jederseits eine Reihe 

 dicht gedrangter Porenpaare, welche, wie gewohnlich, weit kleiner sind als die Poren 

 der paarigen Ambulakra, und sich nach unten zu in eine Reihe einfacher Poren ver- 

 wandeln, die sich zum Munde fortsetzb. Contrary to this statement I find the pores 

 of the frontal ambulacrum rather distantly placed, much less closely than in the 

 Abatus-species; especially towards the fasciole the plates become comparatively high 



