86 ECHINOIDEA. II. 



single plate 2 of the anterior interaiubulacra and by tlie simple pores. The fignre of Offastrr corculiDn 

 given by Loven (On Ponrtalesia. p. 92) is highly interesting as showing the beginning of such an 

 arrangement in the antero-lateral interambulacra ; this form does nndoubtedly show us the way from 

 the ^liiaiic/iyfidii- to the Uncliiiiida- — also tlie pores are very small and the ambnlacral piates high 

 in tilis form, characters pointing towards the UrcL/iii/idæ. bnt the pores are, however, donble as in 

 the trne AiiaiicJiytidæ. 



The Poiirtalcsiida- evidently form anotlier sejDarate branch from the ^iiiaiichytidcr^ with which 

 the\- agree in having the second plate in tlie antero-lateral interambnlacra paired. The main char- 

 acter of this family otherwise is the oral invagination of the anterior ambnlacrnm with the strnc- 

 tnral featnres of the actinal part of the test resnlting therefrom , and tlie vertical position of the 

 peristome. The homoiopodons condition of the tnbe-feet can no longer be regarded as a family char- 

 acter, since Shriiopafagiis is shown to liave penicillate actinal tnbe-feet like the Urcchinidæ and A)i- 

 ancliytidæ: but the simple or even qnite rndimentary pores afford another good distinguishing char- 

 acter between this fainilv and the ^liiaiiLliytidic. in which the pores are donble. Whether we have to 

 seek the transitional forms between the jLi/aiichyfidtr and i\\it /'oiirftilrsildic in snch forms as /w/^z/æs-At, 

 Ilagoioivia or Stegastcr I dåre not have aiiy definite opinion, Ijeing too little acqnainted with these 

 genera; bnt as far as I can see it is rather probable. In any case the Urechinids cannot be regarded 

 as ancestral forms of the Ponrtale.siæ; tlie single plate 2 in the antero-lateral interambulacra is alone 

 a sufficient proof that there cannot be a direct genetic connection between these two families. 



The genus Calyi/uic cannot be referred to either of the two families named, differing from the 

 Urcchinidæ in having the plate 2 of the anterior interambulacra paired, from the Potirtalesiidæ in 

 having no oral invagination and from t\\e Anaiichyfidic in having simple pores. It must then, evidently, 

 form a separate family, Calymnidæ. Whether the marginal fasciole is a family-cliaracter it is impos- 

 sible to decide, as long as this form is tlie only one known of the family; but judging from the other 

 families it will scarcely be more than a generic character. 



The genus Piloiiatccliiiius would be exceedingly interesting, in case the structure of its plastron 

 were really as figured and described by Agassiz in the Panamic Deep-Sea Kchini ; it would then 

 l)e a living representative of the forms in whicli the plastron is still in the primitive condition, known 

 in the Collyritidæ and Cassidiilidæ, and from which the ineridosternous and ami^histernous plastron 

 are later developments. Pilcmatcchiiiiis would then be the most primitive of the recent Spatangoidca. 

 It can, however, scarcely be doubted that Pih-inatccliiints is a true meridosternous form, belouging to 

 the Urcchinidæ. the plate interpreted by Agassiz as the labrum being in faet two piates, a short 

 labrnni foUowed by a larger sternum. — A feature of great interest in Pilciiiatccliiiius is that it has 

 comparatively well developed auricles; this evidently points towards the Gnathosioruata, \{z.th& Holec- 



le Uibriiin ■. This would iiivolve the incorrectiiess of all the cases of Heterononiy in the Interambulacrum i in the Spatangidæ, 

 pointtd out by Loven. Though I cannot foUow Loven in all tliese instances, I think that in niany of them Lovén's inter- 

 pretation of the larger piates as being fused from two or three is quite correct. That the labruni is really a single plate I 

 most decidedly agree with Lambert, and I suppose that I am likewise in accordance with Lambert in rejecting his previous 

 view (Etudes morph. sur le plastron des Spatan gides. p. 63, 72), that in the Spatangidæ the labruni should be considered 

 (Comme une piéce complexe formée par la soudure intime de divers elements enipruntés aux deux series des assnles con- 

 stitutives de l'interradium impair , viz. composed of the two (theoretical) piates a. i and b. 1 and further of the piates a. 2 

 and b. 2, tbe great sterual piates being thus really a. 3 and b. 3. 



