SPONGES, GKAPTOLITE3, CORALS. 



Streptelasina,] 



alternately large and small, slightly dentate, from 45 to 60 of the former in adult 

 examples, while the youngest specimens observed have 30. Cardinal and counter 

 septa long and prominent, alar septa short ; between these primary septa the others 

 are arranged in bundles, the large ones uniting at their inner ends, and are commonly 

 twisted (rarely straight) forming a small pseudocolumella. Lower part of the vis- 

 ceral chamber somewhat filled up with stereoplasma. Tabulae and dissepiments 

 remote and very irregular: 



This species can be readily separated from S. profundum, by the greater curva- 

 ture of the corallum, shallower visceral cavity and more numerous septa, which, 

 on approaching the center of the calyx become more or less twisted. The last 

 named feature never occurs in S. profundum. 



This common coral is more or less abundant at all exposures of the Galena shales 

 throughout Minnesota. Specimens vary from 15 to 45 mm. in length. The large 

 and small septa vary fromGO'to 120. Since so great a variation in the number of 

 septa obtains in this species, it is advisable to consider as synonymous with it, 

 S. crassa, S. multilamellosa and S. parvula Hall. A similar conclusion was reached 

 by Billings in 1863 and by Nicholson in 1875. 



Several immature , individuals of this species have been found growing on 

 Rhinidictya, and occasionally an adult specimen will show traces near the base of 

 the corallum of its former attachment to some bryozoan. That species of this genus 

 are attached to foreign bodies, at least during their earlier growth, is almost certain. 

 As the point of union is very small, it is also quite probable that the individuals, on 

 reaching maturity, became broken off by the weight of the corallum. 



Formation and locality. Common in the Galena shales at many localities in Goodhue, Olmsted and 

 Fillmore counties, Minnesota ; Decorah, Iowa ; Oshkosh, Wisconsin. It is also common in the Trenton 

 limestone at Middleville, Trenton Falls, and elsewhere in New York ; Montreal, Peterboro, and Ottawa, 

 Canada. 



Collectors. E. O. Ulrich, W. H. Scofleld and the writers. 

 Mus. Reg. Nos. 162, 207, 318, 364, 5840, 6750, 7744-7751. 



