112 ROBERT TRACY JACKSON ON ECHINI. 



species. The typical condition is shown in Plate 4, fig. 1. In this external view a number 

 of fine madreporic pores are seen, but no ocular nor genital pores are visible. The specimen 

 was cut in two and viewed from the interior (Plate 4, fig. 2) ; here ocular and genital pores are 

 plainly visible, but in place of a number of fine madreporic pores as seen on the exterior, there 

 is only one large madreporic pore, a condition similar to that in cidarids (text-figs. 59, 60, 

 p. 95); also similar to the condition characteristic of the exterior of the plate in very young 

 Echini (text-fig. 131, p. 129). In Salenia cincta (two specimens) ocular I is insert. In Sakno- 

 cidaris profundi (ten specimens) typically, 70%, ocular I is insert (text-fig. 102), but in three 

 specimens, all the oculars are exsert as in the young and in adults of Mesozoic species. Saleno- 

 cidaris varispina (26 specimens) in 73% has ocular I insert (Plate 4, fig. 6), and 27% are 

 arrested variants with all oculars exsert. In Salenocidaris miliaris (16 specimens) 81 % have 

 ocular I insert, and 19 % all oculars exsert. All the evidence is that modern representatives of 

 the Saleniidae have ocular I insert as a typical character, and more or less frequently have all 

 oculars exsert as arrested variants, like their own young and the adults of Mesozoic species. 



In the Jurassic Acrosalenias a much wider range of characters prevails. The oculars may 

 be all exsert like the Cretaceous Salenias, as seen in Acrosalenia aspera (ten specimens). In 

 Acrosaknia decorata (five specimens) the oculars are all exsert in 60 %, but in 40 % oculars I, 

 V are insert, this as a progressive variant being comparable to the typical character of the 

 next species. In Acrosaknia spinosa (101 specimens) typically, 92%, oculars I, V are insert 

 (text-fig. 103). As arrested variants, in 1 % all oculars are exsert, as in the lower species, 

 A. aspera, and in 7% ocular I is insert like progressive variants of Cretaceous Salenias and also 

 like the typical condition in Recent species (text-fig. 102). In Acrosalenia hemicidaroides 

 (58 specimens) oculars I, V are insert in 86% (text-fig. 104). As arrested variants, 2% have 

 all oculars exsert, 5% ocular I insert. Aberrant variants are rather frequent in this species, 

 7%. Of these, one specimen has oculars V, II insert, one has I, V, III insert, a rare variant 

 in Echini, and two have oculars I, V, II insert. The species Acrosaknia pustulata is more 

 progressive in character. Of 16 specimens, 63 % have oculars I, V insert as a species character. 

 Of arrested variants, only 6 % have ocular I insert; 19% are progressive, with oculars I, V, IV, 

 and 6 % progressive, with I, V, IV, II insert. One specimen is an aberrant variant with oculars 

 I, V, III insert, IV, II exsert, a rare character in Echini. In Acrosalenia pseudodecorata (text- 

 fig. 168, p. 149), according to Cotteau (1875-'80), typically oculars I, V, IV, II are insert. 

 This is interesting, as it is the only regular sea-urchin I know of in which this arrangement is 

 a specific character, although it is a common or rare variant in a good many species; also, it is 

 the same character that is found in the Cretaceous spatangoid Ananchytes ovatus (text-fig. 175). 

 In Acrosaknia wiltoni (12 specimens), oculars I, V are insert as a species character in 58%; 

 five of the specimens showing this character of the bivium insert are in the Jermyn St. 

 Museum, observations on which were kindly sent me by my friend, Dr. Kitchin. Of this 



