1920] Kew: Cretaceous and Cenozoic Echinaidea 



39 



other region, or, on the other liand, that the earlier forms are not 

 preserved to us. 



SCUTELLA SERIES 



So far as known at the present time, the evolution of the genus 

 Scutella on the Pacific Coast begins with the Upper Eocene form 

 Scutella coosensis Kew, which occurs in Oregon. In California only 

 fragmentary remains of Eocene scutellas have been found, and the 

 same is true with the Oligocene, the only known forms on the coast 

 being from Washington. Though scutellas probably existed during 

 the Oligocene in the vicinity of California, up to the present time no 

 traces of them occur. From the scanty evidence afforded by two 

 species found in comparatively distant areas very little can be judged 

 as to the evolution of the Scutellidae prior to the Miocene. 



The Scutella group as a whole is more or less disunited; in only 

 a few cases can any series of species be traced through a continuous 

 section of strata, and there is no evidence of gradational evolutionary 

 changes. In all, about thirteen species are represented, which are 

 scattered throughout the formations over a large part of the Pacific 

 Coast. 



In the phylogenetic series as represented by the chart (see fig. 3), 

 two main series are shown: that of the Scutella blancoensis Kew, S. 

 merriami (Anderson), and S. gabbi (Remond) as forming one main 

 line of descent, and S. coosensis Kew and ^S*. fairbanksi Arnold the 

 other. The S. merriami occurring in the Lower Miocene is closely 

 allied to the S. gabbi found in the Upper Miocene. Both forms are 

 comparatively simple, the later type differing only in minor char- 

 acters, such as a slightly different position of the anus and in its gen- 

 eral shape. 



The first series is represented by forms of small size which show 

 differences in marginal outline and thickness, position of the periproct, 

 and degree of elevation of the abactinal surface. As in the other 

 groups, no continuous series is represented except possibly that con- 

 taining »S'. merriami, S. andersoni Twitchell, and S. tcjonensis Kew, 

 of which the last two are the more highly specialized. Since S. mer- 

 riami possesses a marginal periproct, the supramarginal position in 

 the later species has been considered a retrogressive character in this 

 series. *S^. andersoni has more highly developed characters, such as 

 pronounced marginal notching and a supramarginal periproct. S. 

 tejonensis, in addition, has wide, open, flaring petals whicli extend 



