REPORT ON THE ECHINOIDEA. Ill 



Microcyiihus. 



Mierocyplms, Agassiz, 1841, Val., Anat. Genre. Ech. {iwn Mon. Scut.). 



Microcyphus zigzag. 



Microeyphtis zigzag, Agassiz, 1846, C. E. Ann. Sc. Nat., vol. vi. 

 Station 161. April 1, 1874. Off entrance to Port Philip; 38 fathoms; sand. 

 Station 162. April 2, 1874. Off Ea.st Moncceur Island, Bass Strait; 38 to 40 

 fathoms ; sand. 



Trigonocidaris. 

 Trigonoeidaris, A. Agassiz, 1869, Bull. Mus. Comp. Zool., vol. i. 



Laube has figured among the fossil Echinoidea of Murray Cliffs in Southern Australia a 

 small Sea-urchin (Paradoxechinus novus), of which he gives an enlarged view of a part of 

 the ambulacral and interambulacral areas. I am inclined to consider this interesting fossil 

 as the Tertiary representative of Trigonocidaris. Laube's genus is probably identical 

 with Trigonocidaris, but not having an authentic specimen I am unable to settle this 

 point, and here merely call attention to their probable identity. The difference in the 

 structure of the connecting ridges between the primary tubercles may be due to the state 

 of preservation of the fossil. Laube's genus was described in the Sitzungsb. Akad. Wien., 

 February 1869, while my preliminary description of Trigonocidaris did not appear till 

 October of the same year. 



According to the description of the ornamentation and the detail figures the ridges of 

 Paradoxechinus are double zigzag lines of small tubercles, whQe in Trigonocidaris the 

 zigzag lines uniting the tubercles are smooth ridges forming an irregular network of pits 

 very unlike the regular triangles formed by the ridges connecting the primary tubercles. 

 The only other genus of Echinids presenting such a structural feature is Pleurodiadema of 

 Loriol (an oolitic form), in which, however, this arrangement of the granules or miliaries 

 is in distinct ridges, but in this genus always running horizontally.' 



* Trigonocidaris monolini (PI. VI." figs. 8-10). 



Trigonocidaris monolini, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 203. 



A single specimen from Station 170, measuring 8 mm. in diameter. This species is 

 readily distinguished from Trigonocidaris alhida by the structure of its actinal membrane 

 (PL VI.''' fig. 8); and also by the striking ornamentation of the genital ring (PI. VI. " fig. 9) and 

 by the relatively smaller number of primary coronal plates and their coarser pitted reticula* 

 tion (PI. VI." fig. 10). The ten ambulacral buccal plates of the actinal membrane occupy 

 nearly the whole of the distal edge of the actinal ring, while in specimens of the same 

 size of Trigonocidaris alhida the pairs of plates are separated not only from each other 



I See Cotteau, 'fichinides Nouveaux, Eev. Mag. Zool., No. 97, pi. xxvi. 



