296 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



abundant plates and spicules in the connective tissue which lies beneath the 

 peristome and supports the lip, and also in that which unites the coils of the diges- 

 tive tube. In the regular endocyclic crinoids this organ makes rather more than 

 a single round turn upon itself, and it is the aggregation of calcareous deposits 

 upon its central side which forms the " columella," once regarded as a sand canal. 



INORGANIC CONSTITnENTS OF SKELETON OF ISECKNT CBIXOILS. 



In 1906 Mr. H. W. Nichols published a number of analyses of the skeletons of 

 marine invertebrates, among them one of the skeleton of the pinnulate arms of a 

 crinoid, Metacrinus rotundus, from Japan, in which he found 11.72 per cent of 

 magnesium carbonate (MgCO 3 ) a rather unusual amount. 



This incited my curiosity, and I sent to Prof. Frank W. Clarke, of the United 

 States Geological Survey, for analysis some pinnulate arms of the same species 

 (Metacrinus rotundus) collected by myself in the Eastern Sea in 1906, and in addi- 

 tion pinnulate arms of Heliometra maxima, which I had dredged in very cold 

 water in the Sea of Japan in the same year. Both specimens were air dried from 

 alcoholic material. The analyses were made, under the supervision of Professor 

 Clarke, by Dr. Chase Palmer, and gave the following results : 



Metacrinus rotundus. Locality, Albatross Station 4934; lat. 30 58' 30" N.. 

 long, 130 32' 00" E. (Sata Misaki Light bearing N. 77.5 E., 7 miles distant), in 

 the Eastern Sea off Kagoshima Gulf ; depth, 103-152 fathoms ; bottom temperature, 

 about 56 F. 



CaO=49.95 per cent (equivalent to CaCO 3 89.19 per cent). 



MgO= 4.89 per cent (equivalent to MgCO 3 10.29 per cent). 



Doctor Palmer notes that " this specimen is white and quite free from ex- 

 traneous material." 



It is probable that this individual lived at a somewhat greater depth and in a 

 slightly less temperature than that studied by Nichols, which I assume was a com- 

 mercial specimen obtained through Mr. Alan Owston from Japanese fishermen 

 living at Sagami Bay. 



Heliometra maxima. Locality, Albatross Station 4986; lat. 43 01' 40" N., 

 long. 140 22' 40" E. (Benkei Mizaki Light bearing N. 35 E., 15 miles distant), 

 in Iwani Bay, northeastern part of the Sea of Japan ; depth, 172 fathoms ; bottom 

 temperature, 33.9 F. 



CaO=40.03 per cent (equivalent to CaCO 3 71.48 per cent). 



MgO= 2.68 per cent (equivalent to MgCO, 5.61 per cent). 



Doctor Palmer adds that "this specimen contains much foreign material, 

 chiefly organic. On the basis of purity as found in the other specimen, the content 

 of magnesium carbonate (MgCO 3 ) in this specimen may be accepted as 7 per cent." 



I commented upon these analyses as follows : Heliometra maxima " is the largest 

 crinoid known, measuring about 3 feet across its extended arms. It might be 

 supposed that the comparative openness of its skeleton was due to this very large 

 size, as a result of the deposition of inorganic matter not keeping pace with the 

 rapid increase in bodily size. It is noticeable, however, that the crinoids of the 

 deep seas and from the colder regions have more delicate and more open skeletons 



