(J58 MR. F. J. BELL ON THE ECHINOIDEA. [June 17, 



the eastern coast of America, was first described by Alex. Agassiz, and 

 is distinguished by its form, its small anal system, and the presence of 

 large plates on the buccal membrane, at the point where this structure 

 unites with the test. In his definition of the form l , Agassiz states 

 that " the anal system and the actinostome are comparatively smaller 

 in the West Indian species." In support of this statement he gives, 

 however, only one set of measurements for T. depressus ; but they 

 hardly bear out his proposition, inasmuch as in the specimen described 

 by him, which had a long diameter of 1 27 mm., the anal system mea- 

 sured 9mm. (giving a percentage valueof 7'08), whereas the four values 

 to be gained from his measurement of H. esculenta are respectively 15, 

 9*2, 8'1, and 7*9. The single specimen of T. depressus in the posses- 

 sion of the British Museum gives a percentage value of 6-6 (the anal 

 system measuring 8 mm. and the long diameter 120 mm.). We 

 might, indeed, imagine that a "than" had dropped out in the sentence 

 just quoted, were it not that it does as it stands state fairly enough 

 the comparative relations presented by the actinostome in the two 

 forms therein mentioned. To this structure we will now turn. In 

 Prof. Agassiz's specimens the actinal system measured 29 mm. 

 (percentage value 22*8) in H. depressa, and 26 - 2 mm. (percentage 

 value 22 - 2) in the largest specimen of H. esculenta of which he 

 gives the measurements. The differences here are indeed not very 

 great, but, such as they are, are evidence against Prof. Agassiz. 

 As, however, my remarks are based rather on what I have been 

 able to observe in the specimens in the national collection than 

 on deductions from Prof. Agassiz's measurements, I am able to give 

 in my adhesion to the statement already quoted, that the actinostome 

 is smaller in the West- Indian species; for I find that while the 

 British Museum specimen of T. depressus gives a percentage value 

 of 25 for the actinostome, that of T. esculentus does not exceed 23*2, 

 and may fall as low as 18"8 per ceut. 



T. esculentus and T. angulosus. — The diagnoses of Prof. Alex. 

 Agassiz are notoriously difficult ; but, so far as an attentive study of 

 his remarks on these two species are of value, they appear to me to 

 be convertible into the following propositions : — 



The species T. angulosus is distinguished from the West-Indian 

 T. esculentus by the following points : 



(i.) The tubercles are smaller in size and less in number. 



(ii.) The anal system is comparatively very large, 

 (iii.) The abactinal system is more circular and less pentagonal, 



owing to the smaller size of the genital plates, 

 (iv.) The poriferous zone is much narrower. 



(v.) The actinostome is larger. 



(vi.) The spines are much more slender, 

 (vii.) The anal plates are smaller and more numerous. 



The descriptions are marred by a very remarkable misprint, 

 which states in effect that the specimens of angidosus measured by 

 Prof. Agassiz have a height nearly twice as great as their long 



1 Revision of the Echini, p. 500. 



