G4 CALAMOCRINUS DIOMED.E. 



Griffith * figures a remarkable widening of the stem of a specimen of 

 Toxocrinus (Plate XXVI. Fig. 7), which reminds us of the analogous struc- 

 ture in the Cystids. 



Structure of the Stem. 



Dr. W. B. Carpenter t has figured the structure of the stem of Pentacrinus 

 caput-Medusse, of Pentacriaites briareus, and of another undetermined 

 species of Pentacrinus. 



There are also to be found in the older works of Goldfuss, Quenstedt, 

 Bronn, Zittel, and other palajontological memoirs, a number of figures show- 

 ing the structural details of the joints of the stem and arms of Crinoids. 

 The reticulation of the limestone plates and joints is remarkably uniform 

 in all Echinoderms, showing but little variation, the reticulation, as has 

 been suggested by Zittel, closely resembling that of the Hexactinellidan 

 Sponges. 



Dittmar:|: has figured the stem of a new genus, Porocrinus, in which 

 there are in the stem a large number of fine canals running longitudinally, 

 with a trend towards the exterior, to which lead a number of lateral canals 

 situated in the space between the joints. Although Dittmar says distinctly 

 " statt eines einzigen centralen Nahrungskanal, sehr viele feine runde 

 Kaniile vorhanden sind," yet further on he says " der centrale Kanal-allein 

 zeio-t keine seitliche Abzweigung " ; and the longitudinal section which he 

 gives shows a central canal (p. 39o, Fig. 3). The figure he gives of the 

 surface connecting two joints does not differ from that seen in Calamocrinus, 

 where we find a large number of radiating lamellae, but they alternate with 

 those of the adjacent joint, and lap, and do not correspond, as he says, to 

 leave room for the lateral canals. He has noticed the great irregularity 

 in the intercalation of new lamellie, and this agrees fully with the develop- 

 ment, as I have traced it, in tlie young joints of Calamocrinus. We find 

 in the joints of Calamocrinus (Plate XXV. Fig. 9) the same parabolic 

 arrangement of the limestone cells of which he speaks, but the interstices 

 do not form such regular canals as he describes. He considers the canals 

 as analogous in function to the " Sehnen " of Miiller. 



* A Synopsis of the Characters of the Carboniferous Limestone of Ireland, 1844. 



t Report on the Microscopic Structure of Shells, Part II., Sect. 120, Figs 74-77 Report of the 

 Seventeenth Meeting of the Brit. Assoc, for the Adv. of Science, held at Oxford, June, 1847, London, 

 1848. 



t Alphons von Dittmar, Zur Fauna der Hallsfadter Kalke, 1866, in Benecke, Geog. Pal. Beitrage, 

 Vol. L 



