THE CRINOID UYPOCRINUS. 903 



anal plates no trace remains, but the relatively large size of the 

 opening suggests that some probably existed. 



Oi'namem: : — Beyrich says " Sammtliche Flatten sincl aussen 

 glatt unci scheinen zum Theil von porosem Gefiige zu sein." 

 Kothpletz remarks that his smaller specimen " die porose Structur 

 der Flatten, welche Beyrich an seinen stark abgeschlifFenen 

 Exemplare nur vermuthen konnte, sehr dentlich zeigt." As a 

 matter of fact, the holotype is only " strongly worn down " in one 

 or two places, and it shows the texture of the plates (Fl. XO. 

 hg. 6) no less clearly than the specimen described by Rothpletz. 

 The latter author continues : — " Die Fbrositiit der Flatten wird 

 erkannt an den abwechselnden kleineren und grosseren rundlichen 

 Vertiefungen, welche die Oberflache bedecken. Die kleinen 

 Poren stehen regelmassig und dicht gedriingt, die grosseren 

 liegen vereinzelt dazvvischen und hiiufen sich auf den Radialia 

 nahe den Anzatzstellen und auf den Farabasalia in der Gegend 

 der Buckel." This account applies equally well to the holotype ; 

 but I must add that in neither specimen can I detect any 

 regularity of arrangement in the smaller pores. 



The diameter of the smaller pores is about -075 mm. or more. 

 The diameter of the larger pores is "3 mm. or less. There is 

 every gradation between these sizes. 



This micro-structure of the test is so unusual, if not unique, in 

 its absence of regularity and in the sporadic occurrence of larger 

 pores, that Beyrich's use of the word " scheinen" may have been 

 due to a hesitation as to the true nature of the appearance. The 

 irregular surface, esjDecially in the umbonal region of a basal, 

 markedly resembles some encrusting hydrozoon with autopores 

 and dactylopores. Were the appearances really due to some such 

 encrustation, this would not have been the only occasion on 

 Avhich an echinoderm plate has been described as porous on 

 similar evidence. But in the present instance, where the rough 

 surface has been worn down, the same porous structure is still 

 seen penetrating the plates. The pores ai-e rendered distinct by 

 the infiltration of a reddish iron colouring. 



Since the matrix itself is of a granular micro- crystalline com- 

 position, with darker specks, it is very difficult to discriminate 

 between the matrix and the rough surface of the plates. Beyrich 

 may have been uncertain whether he was looking at the actual 

 stereom or at an imperfectly cleaned surface. The porous 

 substance is of a saccharoida.l appearance, and is easily scraped or 

 broken with a needle, even with a brass pin. It does not cleave 

 with a smooth fracture, as does the denser stereom near the 

 sutures. 



This apparent porosity of the test doubtless weighed with 

 those authors who referred Hypocrinus to the Cystidea, but 

 the structure is really nothing but an exaggeration of that seen 

 in the cup-plates of the larval Anteclon laefore the connective 

 strands of stroma have impressed on the stereom a I'adiate or 

 fasciate arrangement. The exaggeration consists partly in the 

 greater size of the pores, which, as figured by W. B. Carpenter 



